IndigoSplash:

**Which is the appropriate sentence?

If he was a little smarter, he'd be in school.
If he were a little smarter, he'd be in school.**

I believe it is:

If he were a little smarter, he'd be in school.

Here's the scary grammar rule behind it - you have a "Contrary to Fact If Clause" for your sentence. (He is not actually a bit smarter, you just wish he were.) You need to use the Imperfect Subjunctive form of the verb in the "if clause" because the statement is not actually true. The second part of the statement uses the Conditional verb form - "he would be in school."

If you want the easy to remember version, think of the famous phrase: if wishes were fishes, we would never starve.

Sad to say, I was never taught this in English class. I learned it while studying Spanish. (And it wasn't a high level Spanish class.) I learned more about grammar in my Spanish classes than in my English classes.