Table 2. Physical Education Lesson Time in Moderate-to-Vigorous Physical Activity, Evaluation of Effectiveness of Physical Activity Policies, San Francisco, 2010-2011 School Year.

Lesson Time	Elementary Schoolsa								Middle Schools (n = 4)		High Schools (n = 4)
	All Schools (n = 20)		Specialist Schools (n = 10)		Nonspecialist Schools (n = 10)				Mean (SD)	Range	Mean (SD)	Range
	Mean (SD)	Range	Mean (SD)	Range	Mean (SD)	Range	P Valueb	95% CI
Scheduled lesson length (min)	36.4 (7.4)	25.0–55.0	35.6 (6.6)	25.0–55.0	37.3 (8.1)	30.0–55.0	.40	−7.2 to 2.9	50.1 (2.1)	40.0–57.0	58.0 (20.0)c	30.0–95.0
Observed lesson length (min)	31.4 (7.9)	10.0–53.7	32.0 (7.6)	10.0–50.0	30.7 (8.3)	12.3–53.7	.62	−3.6 to 6.1	39.9 (3.6)	28.0–48.3	48.7 (17.8) c>	20.0–90.3
Observed proportion of lesson time in MVPA, %	54.0 (12.9)	22.1–81.0	55.0 (12.9)	22.1–80.0	53.0 (12.9)	25.0 - 81	.55	−.02 to .12	51.2 (12.0)	26.5–76.0	55.7 (18.4)	0.7–79.1
Calculated minutes of MVPA per lesson, no.	16.6 (4.6)	6.0–26.3	17.2 (4.6)	7.0–26.3	15.9 (4.5)	6.0–24.7	.36	−1.3 to 3.6	20.4 (5.2) c , d	10.0–31.3	27.5 (14.1) c	0.3–53.3

Abbreviation: SD, standard deviation; MVPA, moderate to vigorous physical activity.

^a A maximum of two 5^th grade teachers were observed per elementary school, and a maximum of 3 7^th or 9^th grade teachers were observed per school for middle and high schools; all teachers were observed up to 3 times each.

^b P value and 95% confidence interval for difference in means between specialist and non-specialist elementary calculated by linear mixed effects models accounting for clustering by teacher and school; P < .05 indicates significance.

^c Significant difference in means between elementary and middle/high schools,

^d Significant difference in means between middle and high schools.

^e Lesson observation began when 50% of students had arrived at the physical education area.