If he's teething, it hurts to eat, solids especially. As for the high chair - it could just be because he knows you are going to force him to eat when it hurts. Otherwise, it will be just a matter of training him with stuff he likes. You could also use it for painting or coloring to help him get used to sitting there. But, If you're wanting him to only eat in the highchair, then stick to your guns. When, the teething stops it will be easier. Many kids don't like the constraint. They would rather be roaming around playing and exploring or being held. He'll will always do what you expect of him. So, be consisten, be stubborn, and insist on your expectations for everything. As for now, I would back off a little and make sure he's not in pain. I would always ice down their gums right before taking several bites. Then ice it down again. They will cry with the ice, but it will ease the pain when I feed them.