CHICAGO – The nonprofit PTA sued a for-profit rival on Wednesday, accusing it of denigrating the established group in a bid to siphon off members – a dispute that highlights underlying tensions as parents consider changes in how they interact with their children's schools.

The National Parent Teacher Association, an iconic group that's been part of America's cultural backdrop for more than a century, has seen its membership fall by more than half of the 12 million members it had in its heyday in the 1960s. That decline, at least in part, motivated the PTA to file the lawsuit against PTO Today.

The upstart group put itself on a collision course with the PTA by setting itself up as an alternative.