Influence of the quality implementation of a physical education curriculum on the physical development and physical fitness of children

The sample consisted of 146 second-grade classes from 33 quasi-test and 33 quasi-control schools with 950 children in the first group and 994 children in the latter one (Figure 1). The sample included 453 girls and 497 boys in the quasi-test group and 483 girls and 511 boys in quasi-control one. The baseline age in both groups was almost identical (mean = 6.78, SD = 0.30).

In 2008, a questionnaire on school environment was sent to all 450 Slovenian primary schools and was completed by school principals or PE teachers. Among the 199 schools that returned the questionnaire, the majority had PE in the first three grades delivered by generalist teachers, while 33 had PE delivered by specialist PE teachers from the second grade onwards. The second-grade classes from the latter schools were assigned to the quasi-test group. We then paired the quasi-test classes with quasi-control classes from the neighbouring schools to exclude as many environmental factors as possible. PE and classroom teachers both followed the same official PE curriculum and had very similar teaching environments regarding facilities and equipment (all included primary schools have two gyms with standardised equipment), and number of children in the classes (see Figure 1); all classes had three compulsory 45-minute lessons of PE per week.

We used the SLOFIT database to extract data of the eight motor tests and the three anthropometric measurements for every child included in the first, second and third years of schooling. The results of the motor tests were used to calculate the physical fitness index (PFI) and the body mass index (BMI) for every child in all three grades. Baseline and both follow-up measurements took place at schools during PE lessons in April 2007, 2008 and 2009. The SLOFIT system, implemented in 1987 and formerly known as the Sports Educational Chart, is a Slovenian monitoring system of children's motor and physical development. Every April, qualified PE teachers with a completed anthropometry measurement course perform the measurements in all primary and secondary schools as required by the PE curriculum, following the official measurement protocol [38]. The SLOFIT test battery includes eight motor tests (arm-plate tapping (APT), standing long jump (SLJ), polygon backwards (PB), sit-ups (SU), standing reach touch (SRT), bent arm hang (BAH), 60-meter run (60 m) and 600-meter run (600 m)), and three anthropometric measurements (height (BH), weight (BW) and triceps skinfold thickness (TSF)). Measurements are always organised in school gyms between 08:00 and 14:00. Subjects were weighed barefoot in their shorts and T-shirts to the nearest 0.1 kg with portable scales of various brands; height was measured with stadiometers of various brands to the nearest 0.1 cm; triceps skinfold was measured with Holtain-Tanner callipers to the nearest mm. All instruments were calibrated once at the beginning of the measurements. Data were checked to detect coding errors. In order to include and evaluate the children's measurements in the SLOFIT system, and to use the data for scientific purposes, children need the written consent of their parents; throughout the existence of this system, the response rates in primary schools have remained above 94%. The SLOFIT database currently includes more than five million sets of measurements and grows at a rate of approximately 210,000 sets of measurements per year.

All statistics were computed using the PASW 18 for Mac statistical software package (SPSS Inc., Chicago, IL). Since this was a quasi-experiment, we used the Linear Mixed Model procedure to test the influence of specialist PE teachers' teaching (PTE) on the physical fitness and physical development of children by excluding gender and age, and by using teacher and age in months as a fixed effect. Because there are individual differences among PE teachers, PTE was also used as a random effect along with schools. The physical fitness of children was assessed according to PFI, which was computed by averaging the z-scores of all eight motor tests. BMI was calculated from body weight and height, but the BMI z-score was used in the analysis. Linear Mixed Models were used to test for dependent variable PTE with independent variables. The latter consisted of two main primary outcome variables (PFI and BMI z-score), and secondary outcome variables (z-transformed results of individual motor tests in all three grades). Preliminary tests to identify possible effects of gender and school grade on PFI, BMI and secondary outcome variables were not performed, since z-scores of all tests were calculated by the RANKIT procedure according to school grade and gender. Several models and unstructured covariance matrix were tested separately for each dependent variable to find the best-fit model.

This study was funded by the Slovenian Ministry of Education and Sport and was approved by the Faculty of Sport of the University of Ljubljana ethics committee. Written positive consent of parents was provided for the use of data in scientific purposes. All procedures and methods in this study conformed to the ethics guidelines established by the World Medical Association's Declaration of Helsinki and the subsequent revisions.

There are limitations to our study, and care should be taken in generalising its results to different countries, since there are considerable differences in the organisation and contents of PE curricula worldwide. The study was a quasi-experiment and did not control for many important environmental and social factors influencing the physical and motor development of children, although we tried to control for those factors by sampling from neighbouring schools from similar social and natural environments. The schools from the intervention groups were not randomly selected but were included based on the return of the school environment questionnaire. We were also unable to gather the information on teachers' actual PE planning and teaching competencies, which surely influence the quality of curriculum delivery. We were not able to gather the information on the intensity levels of PE lessons, which undoubtedly affect the health outcomes. Also, we gathered no information on the actual role of generalist teachers in PE planning and the delivery of PE lessons by PE specialists. In our experience, classroom teachers are present in the gym with the PE specialist but limit their activity to occasional help in setting the teaching environment and managing children who do not participate in the activities due to health and other reasons; they leave the planning and/or delivering the lessons to the PE specialists. We are aware that the level of physical fitness and body composition are not the only factors determining physical activity and consequent health outcomes in adult life, but the nature of our study did not allow us to gather additional information on the psycho-social effects of quality PE. Although the quasi-test and control groups had identical amounts of PE lessons per year, we have no information whether the children's out-of-school activities affected the results. Finally, we acknowledge that the quality of PE teaching does not rely solely on the level of professional competencies acquired in the teaching education programmes, but also on the level of social and other competencies of teachers that remained unknown to us.