My children have been in a small private school with relatively small class sizes. aeh has summed up the things to think through re the program well - I'll add a few things that I'd suggest you look into re the school itself.
It's important to not just look at the academics, but with small private schools you'll also want to look at the business side of things. Being a small school may be great, but I'd ask these questions of the school:
1) What is their goal for # of students / grade and goal for # of students in school?
2) Why, after 10 years in operation, do they only have 10 enrolled students?
3) What are the admissions requirements (actually ask, don't just rely on what their website says or what first is told to you). If there is testing involved or required test scores, go ahead and ask if all of the students currently enrolled had the required test scores.
4) Ask how many students they had last year, and ask what their yearly turn-over rate is, and why students/families leave the school.
5) How long has the head of school been in place? How long has most of the staff been teaching at the school? You're trying to judge turn-over here.
6) They may not answer this, but I'd ask anyway - how much do they pay their teachers relative to your local public schools?
7) Do they rent or own the building they are in? How long is their lease? Have they been in the same location for the past 10 years?
8) Who is on their Board of Directors? Is it primarily parents? Community members? A mix?
9) How does their tuition compare with other local private schools? If it is significantly higher or lower, ask why. This is a good set of data to have - if you don't know what other schools are charging for tuition, check into it - this is info you can often find online.
10) How do their teachers' salaries compare with teachers' salaries in your local school district?
11) What percentage of the school's budget goes to teacher's salaries vs school supplies vs building expenses vs marketing? (They might not share that info with you, but it is interesting info to have).
12) Where does the money required to run the school come from? Obviously part of the money comes from tuition, but with such a small school tuition alone isn't going to be anywhere near enough (unless it's exorbitant tuition, which would most likely price the school out of business). What percentage comes from fundraising, and what are the expectations on each family for giving expectations and for helping with fundraising.
A few other things I'd consider asking:
1) How does this school's curriculum compare to your state's curriculum standards and your local school district's curriculum?
2) If it's a school for lower grades (no secondary or high school), I'd ask where the kids who leave go to high school typically, and how they fit in, what the issues are etc.
3) What is the educational background of the teachers? Which teachers will your child be working with?
Please know that none of my questions above are meant to be discouraging - the info is good to have. I've been involved with three different private schools, two of which had significant financial challenges that were definitely not advertised to prospective families

Also please know - it's very possible to have a school that looks horrible in terms of financial set-up, yet is an excellent school day-to-day for students. The risk is - what happens if a school goes under and your child has to switch tools again.
Good luck making your decision!
polarbear