The main purpose of the present study was to assess usual physical activity (PA) patterns of school children. The study was carried out with 49 boys and girls (mean age of 10 years) in 4th grade of two schools in Vila Nova de Gaia/Portugal. Children wore a portable accelerometer device (Tritrac-R3D) on the waist for 5 days. Statistical procedures included descriptives (means, standard deviation, frequency) and independent t-test. The main results were as follows: (1) during the school period, PA level was low, with children not doing the daily minimum of 30 minutes of moderate to vigorous PA; (2) boys showed a higher pattern of moderate to vigorous PA than girls during recess period; (3) children, even in organized physical education (PE) classes, demonstrated a low PA pattern, with less of 50% of the total PE class time in moderate at vigorous PA; (4) there was no difference in energy expenditure when comparing PE class and school recess.