My daughter graduated from WPI. She had some professors who were difficult to understand because of their accents. However, she found office hours to be helpful despite this. Perhaps those professors were easier to understand one on one. I attended RPI and I can guarantee the situation would be the same for your son there as at WPI. I had the same experience at my undergrad school, which was a large state school. Over time, I became comfortable with certain accents and speech patterns.
You really can’t avoid it. But, you can adjust to it.