Who in the WORLD says that all steps are cheatmates? How about if they simply care about the kids? How about if thier own kids are involved in the school? How about if they're stay-at-homes and have more time to spend with the kids? How about if they're a step-FATHER and the only of the other 3 parents (bio and step) who has a clue about math, or who went to college, or who knows about sports schoarships enough because they went to college on one?
How about if the step is financing the child's attendance at the private school or will be financing it at the college?
There are ALL KINDS of reasons that a step might choose to show up and it's usually NOT that they're interested in going to a boring old parent-teacher conference just for the purpose of messing with the ex. I'm not saying that there are not a few steps for whom that's their purpose in life, but most of us did NOT cheat, most of us do NOT want to upset the ex, most of us DO care about the kids and usually we bring something to the table that the other parents who are alreayd present in the kids' lives havent' already brought.
Bio parents who are upset about a step's attendance at these functions are letting thier own personal jealousies get in the way of doing right by their kids, and it's wrong... but because theyr'e the bio parent, it's the step's job to be the "bigger person" and step back if the bio parent can't manage thier own emotions about the issue.