I generally build the school early, in year 2, after shelter & my 1st Forest Cluster. The only other buildings that I may build before it might be a Tailor and/or Blacksmith, and, if you're playing a "Hard" start, perhaps a Barn. Citizens that enter the labor market at 11 spend 70ish years making poor use of their tools. Send 'em to school, & they'll spend 8ish years not breaking any tools at all, and the rest of their lives making the best of their tools.
Now for the problem of an initial labor shortage. You should be getting your early food from Gatherers & Hunters. They may be inefficient on space, but they are very efficient on labor. Just make sure that your Forest cluster has as few other buildings in it's radius as possible. While fishermen can be tempting as your first source of meat, they do nothing to help keep your people clothed. Hunters produce meat and leather.
You should also note that early in the game your Tailor, Blacksmith & Builder professions are hardly full time jobs. Feel free to give a builder part time work in these two buildings. I've also been known to utilize a woodcutter that has caught up on his stockpiling of firewood in these two rolls also.
Response to questions in comments:
Forest Cluster: 4 buildings at most; Forester, Gatherer, Hunter, & Herbalist. Your Stockpile, Barn & some houses are placed just outside cluster radius. Optional Woodcutter placed facing the stockpile. Supplies basic food & fuel to keep you alive through the 1st winter, along with basic health care. Gatherers & Herbalists are dependent on mature trees. Hunter just needs open space.
Tailor & Blacksmith: Along with your School, 2nd Tier Priorities. Definitely before your starting supply runs out. I consider Tools, Cloths & Education my 2nd tier priorities in order to keep my town working efficiently. Cloths keep your people from walking home frequently to warm up. While they are on the job, Tools & Education keep them at their best. 3rd Tier priorities might be happiness, food diversity (grain in particular), improved Tools/Cloths, and Fire Prevention.