(1) Was it an accredited Montesorri school? There is a wide range of quality within the Montesorri programs and the quality of the teachers is a real difference marker (in terms of them helping guide childrens desire to learn).
(2) What is your comparative benchmark (ie how do you know you would have done better at another school?) and what is your metric for success (how you performed for tests at school or how you developed as a human? Do you find you have a natural curiosity in the world/learn?)
(3) What type of school did you transition into and at what age?