| Notre Dame Preparatory School | 0.8 |
Regular elementary or secondary | 10-12 | 26 | 4.4 | Roman Catholic |
| Cushing Academy | 7.7 |
Regular elementary or secondary | 9-12 | 436 | 7.2 | Nonsectarian |
| Trivium School | 9.2 |
Regular elementary or secondary | 7-12 | 76 | 6.7 | Roman Catholic |
| Groton School | 10.4 |
Regular elementary or secondary | 8-12 | 353 | 4.6 | Episcopal |
| Lawrence Academy | 11.2 |
Regular elementary or secondary | 9-12 | 400 | 3.1 | Nonsectarian |
| New River Academy | 11.2 |
Alternative/other | 9-11 | 8 | 2.7 | Nonsectarian |
| The Winchendon School | 14.5 |
Regular elementary or secondary | 9-12 | 250 | 7.2 | Nonsectarian |
| Caritas Academy | 16.1 |
Regular elementary or secondary | 8-12 | 28 | 2.6 | Christian (no specific denomination) |
| Hudson Catholic High School | 17.1 |
Regular elementary or secondary | 9-12 | 135 | 9.2 | Roman Catholic |
| The Victor School | 18.5 |
Special education | 8-12 | 49 | 5.6 | Nonsectarian |
| St Peter-marian Catholic Jr-sr High School | 18.8 |
Regular elementary or secondary | 7-12 | 913 | 17.6 | Roman Catholic |
| St John's High School | 19.8 |
Regular elementary or secondary | 9-12 | 965 | 14.6 | Other |
| Wayside Academy | 20.1 |
Special education | 8-12 | 20 | 4.0 | Nonsectarian |
| Notre Dame Academy | 20.3 |
Regular elementary or secondary | 9-12 | 285 | 8.8 | Roman Catholic |
| Glenhaven Academy | 20.7 |
Special education | 8-12 | 24 | 4.0 | Nonsectarian |
| Middlesex School | 21.8 |
Regular elementary or secondary | 9-12 | 358 | 6.1 | Nonsectarian |
| St Mary S Jr/sr High School | 22.6 |
Regular elementary or secondary | 7-12 | 144 | 9.6 | Roman Catholic |
| St Mark's School | 22.6 |
Regular elementary or secondary | 9-12 | 359 | 5.4 | Episcopal |
| Holy Name Central Catholic Jr/sr High School | 23.1 |
Regular elementary or secondary | 7-12 | 707 | 15.7 | Roman Catholic |
| Lowell Catholic High School | 23.3 |
Regular elementary or secondary | 9-12 | 330 | 15.5 | Roman Catholic |
| Concord Academy | 23.4 |
Regular elementary or secondary | 9-12 | 364 | 7.6 | Nonsectarian |
| Walden Street School | 23.8 |
Special education | 7-12 | 27 | 4.8 | Nonsectarian |
