Which price applies to my school?

The tier is set once, when the limit is first crossed, and never changes afterwards. The Martialnote plan screen shows your school's tier:

• Growing school: one of the first two measurements was 25 or less. $14.99 per month, for life, taxes included; no spot is taken.
• Founder spot: a large school from the start, if one of the 25 spots is left. $14.99 per month, for life, taxes included.
• Regular plan: $24.99 per month, taxes included.

As long as no tier is set (free school), the screen shows the two possible prices and the rule. A founder spot is taken at the first successful payment and kept for life (see the FAQ "Will I keep my founder rate?"). Each rate also exists yearly: $149 (founder and growing school) or $249 (regular), taxes included.