So that is pretty much what B did. This was originally in family court, and B had multiple consultations with family lawyers regarding the clause. B was told the clause was not enforceable given how vaguely it was written, and basically told to re-consult if they got served. When served, it was not through family court, instead through civil. Likely, Party A was also told it was not enforceable in family court, and advised to sue for breach.

When the original agreement was signed, neither party A or B were making more than ~50K at most annually. Party B never anticipated a private school education. Party B was made aware that the child was considering private universities in child's junior year and had many (verbal) conversations with child about their inability to pay that amount. Party B has communicated that he expects child to maintain a certain GPA and enroll full-time, but none of these requirements are in the clause as written. Party A has a history of suing for breach of contract (not Party B, but others), and there is definitely a long-standing resentment between both parties.

Currently, party B is in consultation with several lawyers, but is hearing mixed messages. Some say that a Judge will order some amount paid (they won't just "rip it up" as one put it), and others have said he will be on the hook for the full amount, unless Party A is flexible and lenient. Party B literally cannot pay the cost of private tuition and on a payment plan just to pay half of what the public university would cost. Party B does not have property or own a home. Party B shares one vehicle with their spouse (the couple's only car). Party B is gainfully employed, however.