Preston Elementary: math

The shaded band is this school's normal range. If nothing about how it works changes, nearly every future year should land inside it. Zero means the typical student just meets the state standard. The small numbers under the years are how many students were tested.

Step 1 · Each year's result

For each grade tested, take the average (mean) scale score from the California Department of Education's results file, and subtract the lowest score that counts as "Standard Met" for that grade. That is the grade's distance from standard. Weight each grade by its share of the students tested, then add the grades up. Grades where the state hides the average because ten or fewer students tested are left out entirely.

2015 from sb_ca2015_1_csv_v3.zip

Grade	Line in file	Average score	Standard Met	Distance	Students	Weighted
3	67,363	2380.5	− 2436	−55.5	× 106 / 283	−20.8
4	67,364	2410.0	− 2485	−75	× 101 / 283	−26.8
5	67,367	2439.6	− 2528	−88.4	× 76 / 283	−23.7
Sum, rounded to a whole point						−71

2016 from sb_ca2016_1_csv_v3.zip

Grade	Line in file	Average score	Standard Met	Distance	Students	Weighted
3	62,448	2395.5	− 2436	−40.5	× 87 / 294	−12
4	62,450	2404.1	− 2485	−80.9	× 108 / 294	−29.7
5	62,452	2430.3	− 2528	−97.7	× 99 / 294	−32.9
Sum, rounded to a whole point						−75

2017 from sb_ca2017_1_csv_v2.zip

Grade	Line in file	Average score	Standard Met	Distance	Students	Weighted
3	64,239	2387.9	− 2436	−48.1	× 107 / 297	−17.3
4	64,242	2421.7	− 2485	−63.3	× 92 / 297	−19.6
5	64,244	2427.2	− 2528	−100.8	× 98 / 297	−33.3
Sum, rounded to a whole point						−70

2018 from sb_ca2018_1_csv_v3.zip

Grade	Line in file	Average score	Standard Met	Distance	Students	Weighted
3	64,347	2381.3	− 2436	−54.7	× 91 / 286	−17.4
4	64,349	2421.3	− 2485	−63.7	× 106 / 286	−23.6
5	64,351	2441.2	− 2528	−86.8	× 89 / 286	−27
Sum, rounded to a whole point						−68

2019 from sb_ca2019_1_csv_v4.zip

Grade	Line in file	Average score	Standard Met	Distance	Students	Weighted
3	64,714	2379.6	− 2436	−56.4	× 106 / 292	−20.5
4	64,715	2417.4	− 2485	−67.6	× 88 / 292	−20.4
5	64,716	2455.8	− 2528	−72.2	× 98 / 292	−24.2
Sum, rounded to a whole point						−65

2022 from sb_ca2022_1_csv_v1.zip

Grade	Line in file	Average score	Standard Met	Distance	Students	Weighted
3	64,781	2385.9	− 2436	−50.1	× 85 / 253	−16.8
4	64,782	2399.7	− 2485	−85.3	× 81 / 253	−27.3
5	64,783	2379.8	− 2528	−148.2	× 87 / 253	−51
Sum, rounded to a whole point						−95

2023 from sb_ca2023_1_csv_v1.zip

Grade	Line in file	Average score	Standard Met	Distance	Students	Weighted
3	64,778	2389.6	− 2436	−46.4	× 78 / 249	−14.5
4	64,779	2410.8	− 2485	−74.2	× 91 / 249	−27.1
5	64,780	2403.6	− 2528	−124.4	× 80 / 249	−40
Sum, rounded to a whole point						−82

2024 from sb_ca2024_1_csv_v1.zip

Grade	Line in file	Average score	Standard Met	Distance	Students	Weighted
3	64,746	2385.2	− 2436	−50.8	× 77 / 246	−15.9
4	64,747	2419.1	− 2485	−65.9	× 82 / 246	−22
5	64,748	2411.0	− 2528	−117	× 87 / 246	−41.4
Sum, rounded to a whole point						−79

2025 from sb_ca2025_1_csv_v1.zip

Grade	Line in file	Average score	Standard Met	Distance	Students	Weighted
3	64,502	2405.8	− 2436	−30.2	× 61 / 217	−8.5
4	64,503	2413.1	− 2485	−71.9	× 67 / 217	−22.2
5	64,504	2424.6	− 2528	−103.4	× 89 / 217	−42.4
Sum, rounded to a whole point						−73

Step 2 · The average and the normal range

Average: add the yearly results and divide by how many there are. −71, −75, −70, −68, −65, −95, −82, −79, −73 → −75.3
Typical year-to-year change: how far the result moved from each year to the next, ignoring up or down. 2015→2016: 4 · 2016→2017: 5 · 2017→2018: 2 · 2018→2019: 3 · 2019→2022: 30 · 2022→2023: 13 · 2023→2024: 3 · 2024→2025: 6 → average 8.3
Normal range: multiply the typical change by 2.66, then add it to the average and subtract it. 8.3 × 2.66 = 22.1. Upper limit −53.2, lower limit −97.4.

Why 2.66? It is the standard factor from quality control, the work of Walter Shewhart and W. Edwards Deming. It turns "how much the result typically changes in a year" into "how far it can wander by chance alone".

Years with no result (no state tests were given in spring 2020) are skipped: the year-to-year change runs from the last year with a result to the next one.

Step 3 · Free or reduced-price meals

The share of enrolled students eligible for free or reduced-price meals. From 2014–15, 2015–16, 2016–17, 2017–18, 2018–19, 2020–21, 2021–22, 2022–23, 2023–24, 2024–25, 2025–26.