What exactly did the father do that got him banned from campus? I can't imagine they did this just because he called them or wrote them a letter to try to get his son out of a class.
If I recall, the father objected to the fact that his son was being taught pro-homosexual curriculum at school. He went to a school meeting and demanded to have his son removed from class when these topics were discussed. The school official refused to remove his son, and the dad refused to leave school property. They had him arrested.
Note the links in my post above. There are many, many articles about this on FR.
Hard to believe, yes, but............believe it. It's exactly what happened. The administrators and teachers say "it's legal now, get over it."