"My daughter (who is now twelve) has been taking classes at Firecracker for the last two years, first in their regular 6th-8th grade class, and then in their Math in Motion class, which introduces kids to the core concepts of calculus. We've really liked Firecracker's approach as a complement to regular school math. Their classes really show how mathematicians think and solve problems in a deeper way than kids are typically exposed to in school.
In the main Firecracker classes, the teacher typically starts with something engaging and accessible, like a physical puzzle or simple game, then uses it to illuminate abstract mathematical concepts like parity or the pigeonhole principle. In addition to asking questions for the kids to figure out, the teacher encourages the kids to formulate interesting mathematical/logical questions about the topic themselves and work with each other to explore them both intuitively and logically. I particularly like that the teachers are good about giving them space to try different paths to solving a problem before giving them guidance towards the solution if they don't figure it out on their own.
With Math in Motion, the teacher started by explaining the concept of limits in an intuitive way, then introduced differentiation and integration through concrete examples of instantaneous speed and area measurement. This class does require the kids to have some basic familiarity with algebra but really manages to convey the key ideas without getting too bogged down in symbol manipulation.
Overall, I think Firecracker does a great job of showing what real mathematical problem-solving is like, and how fun it can be, beyond the mechanical aspect that tends to get emphasized in schoolwork."