Table 3 Logistic regression analyses on low academic performance by grade n = 1663

Sex (girl/boy)

15.8/19.3

0.78 (0.55–1.12)

0.79 (0.54–1.16)

19.0/17.8

1.08 (0.76–1.53)

1.30 (0.89–1.89)

 < 6:30 a.m.

14.7

1

1

14.7

1

1

 6:30 to < 7:00

19.5

1.40 (0.97–2.03)

1.27 (0.86–1.89)

21.3

1.56 (1.08–2.25)

1.38 (0.94–2.03)

 ≥ 7:00

40.0

3.88 (1.67–9.00)

3.47 (1.41–8.53)

27.5

2.19 (1.04–4.63)

1.84 (0.85–4.43)

Skipping breakfast (yes/no)

32.4/16.9

2.37 (1.16–4.83)

1.27 (0.56–2.87)

23.3/17.9

1.39 (0.78–2.47)

0.99 (0.53–1.84)

Screen time on week day (≥ 2 h/< 2 h)

23.5/14.4

1.82 (1.27–2.63)

1.45 (0.98–2.15)

21.3/16.2

1.40 (0.98–1.98)

1.29 (0.89–1.88)

 Very often

14.1

1

1

17.1

1

 Often

16.6

1.22 (0.77–1.91)

1.49 (0.92–2.40)

20.5

1.25 (0.81–1.92)

1.22 (0.78–1.90)

 Rarely

23.8

1.90 (1.16–3.13)

1.84 (1.09–3.12)

17.0

0.99 (0.62–1.58)

0.99 (0.61–1.62)

Bedtime on week day (late/not late) late: ≥ 10 for junior and ≥ 10:30 for senior grades children

22.3/16.9

1.41 (0.84–2.38)

0.92 (0.51–1.64)

19.7/18.2

1.10 (0.69–1.78)

0.86 (0.51–1.46)

Daytime sleepiness (yes/no)

23.6/16.7

1.54 (0.95–2.52)

1.41 (0.83–2.40)

19.4/18.1

1.09 (0.71–1.66)

0.98 (0.63–1.53)

Obesity (yes/no)

20.6/17.3

1.24 (0.67–2.30)

1.00 (0.52–1.93)

20.0/18.3

1.12 (0.59–2.10)

1.17 (0.60–2.27)

Cram school (no/yes)

18.6/14.2

1.38 (0.87–2.17)

1.01 (0.62–1.66)

19.6/15.0

1.38 (0.91–2.09)

1.03 (0.66–1.61)

Study duration at home (< 1/≥ 1 h)

19.7/11.1

1.98 (1.23–3.19)

1.81 (1.08–3.02)

23.5/13.2

2.02 (1.41–2.90)

1.92 (1.29–2.85)

Paternal smoke (yes/no)

23.3/13.4

1.96 (1.37–2.82)

1.67 (1.13–2.48)

21.2/16.0

1.41 (0.99–2.00)

1.27 (0.87–1.84)

Maternal smoke (yes/no)

35.7/15.5

3.03 (1.86–4.94)

2.28 (1.32–3.94)

27.6/17.2

1.83 (1.13–2.97)

1.56 (0.92–2.64)

Subjective SES

 High

14.5

1

1

13.3

1

1

 Middle

17.5

1.25 (0.80–1.95)

1.15 (0.72–1.84)

20.2

1.65 (1.04–2.59)

1.62 (1.02–2.58)

 Low

21.3

1.59 (0.97–2.62)

1.38 (0.82–2.34)

20.4

1.66 (1.00–2.77)

1.52 (0.92–2.57)