In international comparison, school entrance examinations differ in their form and implementation from country to country. Because of methodical differences, a direct comparison of impairments reported in different studies is difficult. Previous research has tended to focus on only one or two areas of delays rather than conducting a complete assessment of multiple dimensions [7–20, 26–31]. In this respect, our study provides a more comprehensive perspective.
Strengths and limitations of the study
The major strength of this study is the large, locally representative sample from a clearly defined geographical area. Since examinations used for assessment of developmental delays were mandatory before school enrolment, the selection bias was minimised. Furthermore, the assessment of developmental delays was conducted by a single team using standardised methods, preventing inter-observer variation. However, there are also several limitations. Data from the studied population might not be representative for the whole Germany – in fact one can expect differences based on variation in social status and local ethnicity mix. Furthermore, we were not able to assess the parental socio-economic status, which is potentially an important confounder of childhood development. Also, we were not able to study the consequences of the observed delays for the long term development. This should be subject of additional studies in the future.
Prevalence of development delays
In 2003, a taxonomy and assessment protocol for developmental delays was published by American medical specialists . Based on this classification of “global development delays”, there were the domains of “gross/fine motor”, “speech/language”, “cognition”, “social/personal” and “activities of daily living” [7, 30, 31]. The nomenclature in our study was based on the first four “domains”, but used twelve “subdomains” of development following the local German conventions.
In our study population, approximately every 16th child showed impairments in “gross motor skills”, every 8th child in “fine motor coordination” and slightly less than every 10th child in “grapho-motor coordination”.The rates of delays observed in our study for gross motor coordination were lower and for “fine and grapho-motor coordination” were higher than the rates for the whole of Bavaria. For comparison, 84.7% of 129,597 preschool children in Bavaria in 2004–2005 were able to stand on one leg (a test for gross motor coordination) and 90.8% were able to make a regular hand-coordination-test (a test for fine- and grapho-motor development) . Similar prevalences were found in health reports from Baden-Württemberg (in 1998: 6.5% for gross motor coordination, 4.5% for fine body coordination and 7.5% for grapho-motor coordination)  and from Hesse (disorders of “coordination” for the years 1998–2005 on average around 8.5%) . It is interesting that according to the results of the Early Childhood Longitudinal Study Birth Cohort (ECLS-B), in which children born in 2001 were assessed with respect to their development by three consecutive surveys over six years (preschool wave 2005/06; kindergarten wave 2006 and 2007), partly a significantly higher prevalence of impaired gross motor skills was found . This difference in the prevalence between the Bavarian and U.S. children may have been caused mainly by different study designs: American children were examined methodically in a highly differentiated way, while the school entrance examinations in Germany were just screening examinations.
Problems of pronunciation were the most common developmental delay in our study. In the domain of “speech”, delays in “grammar” and “rhythm of speech” were less common, with all other types of impairment being far less frequent. Comparatively lower rates for disorders of language (1999: 0.4% in “rhythm of speech” and 2.2% for “dysgrammatism”) were found for the State of Baden-Württemberg in previous studies . In contrast, in Hesse, significantly higher prevalences were observed, with approximately 11%-15% of the children having delays in speech in the cohorts of 1998–2005 . The main reason for differences may be the different tests used in school entry examinations in the various states of Germany.
The high prevalence of over 10% for delays of memory and concentration was unexpected, whereas the frequencies of 3.2% to 6.8% for the remaining four subareas of cognitive development were not so surprising given previous findings . Our findings are in clear contrast to reports from the City of Bonn for 2001–2005 (2001: 23.6% vs. 2002: 27.5% vs. 2003:18.9% vs. 2004: 23.2% vs. 2005: 16.3%) , and for the District of Mettmann for both years 2000 and 2003 (20.1% vs. 22.2%) for the subarea of “visual perception” . Generally, the investigation of cognitive delays in preschool children did not receive sufficient attention over a long time period . Only recently the situation is changing .
We identified problems of psychosocial development in every 15th child in our survey. Until recent years, there appears to have been little interest in the assessment of psychosocial impairments. To some degree, psychosocial adjustment has been seen as a vague criterion, difficult to operationalize and not suitable for objective quantification. Nonetheless, it has become clear that it forms an important part of child development, and attempts to assess it are important . Substantial differences were found in the rates of psychosocial problems in other regions in Germany in data published by Public Health Services. In the State of Hesse, 4.5%-5.0% of children had disorders of psychosocial functioning , compared to 8.3% for the State of Schleswig-Holstein and 13.6% in the District of North Friesland . Thus, our prevalence figures are on the lower end in comparison with other regions in Germany. However, different methodologies and diagnostic approaches make direct comparison of these figures difficult. Developing more uniform and standardised assessment tools and diagnostic categories would be important to collate data from different regions and countries, and effectively utilise it for research and public health interventions.
Factors associated with development delays
Many factors negatively affecting child development have been identified in the literature, however the precise magnitude of effects remains difficult to establish. Some attempts to measure these influences have been made over recent years. The effect of visiting a kindergarten , the influence of migration status  and the effects of selected behavioural and environment-related factors  on the development of preschool children were estimated. However, since these studies were all from the district of Dingolfing-Landau, it is not clear to what degree the same factors operate in other regions of Germany or in other countries.
Interesting aspect are the effects of age. The basis for assessing the level of development were the so-called milestones of child development . These developmental milestones describe the acquisition of skills up to a defined age of the child [37, 38], and 95% of children in the targeted age group are expected to have these skills. Given the reference to age, the younger children at the school entry examination might not developed yet the required skills . Children with many or substantial delays will not be recommended for school entrance, but rather asked to delay the start of school for one year. Still, some children with developmental delays enter school and this is the group which would potentially benefit from interventions following school entry examination. In contrast, higher risks for the oldest group were rather surprising. One possible explanation is that there was some selection bias and those who were older at examination were not included in an earlier examination due to a perceived immaturity. In such case, the developmental delays identified in this group might indicate a more serious problem than among the younger children who might just be too young at the time point of examination and obtained the required skills shortly thereafter.
The strongest and consistent association we detected was related to the effect of sex on development. More boys than girls were affected by disorders of development in all areas we tested. This higher prevalence for delays in boys has been a consistent finding in the literature on childhood development . A sex ratio of 1 to 2–4 for girls to boys has been already described for most developmental disorders in the previous analysis using a subset of the current data . Our current analysis provided additional insights into how sex affects specific subareas of functioning. Male gender increased the risk of developmental impairments by 38%-222% for all subareas of development. In addition, only small changes of this effect were found in the adjusted regression models. The exact reasons for this sex differences in development have not yet been established, though many theories have been proposed .
In previous research, we studied the effect of having migrant status (non-German nationality) on developmental disorders . We showed that more children with a non-German nationality demonstrated delays in motor, cognition and psychosocial development than other children. The elevated risk for preschool children with a non-German nationality in the current study in ten of twelve subareas of development was not unexpected. However, this indicated that among migrant children there can be specific stressors and developmental impediments that warrant further exploration and possibly tailored interventions. No doubt, one important reason for this observation can be a language barrier, which may be an important risk factor for some developmental delays, but may also make the assessment process biased.
In the past, primarily psychologists analysed the subject of the influence of siblings on child development [40, 41]. Until a few years ago, no significant interest was paid from the public health point of view to the influence that the presence or absence of siblings has on child development in this age group. Thus, only a small number of reports in public health area can be identified which explored this issue [14, 32], but the specific effect on the prevalence of developmental delays in the target group of school beginners has not been examined in a quantitative way as done in this study. Having siblings was not associated with most areas of development apart from pronunciation difficulties. This finding persisted despite a simultaneous adjustment for migration background. This contrasts with a study by Minnett et al. who found positive influence of siblings on development of children . Our findings were possibly affected by the fact that we could not adjust for socio-economic status.
School entrance examinations were carried out during the period from November to April of calendar year. New school year in Bavaria begins always in the middle of following September. Thus, the preschoolers were assessed on average six months before entering primary school. During this period there is enough time for support measures if developmental delays were diagnosed in school entry examination. In this context, it should be noted that school entry examination is the only mandatory testing in the Federal Republic of Germany for children, but no standardised intervention measures are implemented for those who do not pass the examination or display deficits. For children with developmental deficits a specialized treatment can be recommended on individual basis, for example speech therapy, occupational therapy or supportive courses in sports.