Now he is helping to train them as the senior mentor at Ysgol Cynfran in the village of Llysfaen, near Colwyn Bay.
And while a new report suggests many primary schools are subsidising teacher-training placements (see page 1), Cynfran fares relatively well.
It receives around pound;800 for each student from Bangor university. That compares to an estimated actual cost - mainly in staff time - of pound;1,060. "I've never complained about funding because it's beyond my control," said Mr Williams. "But I'm grateful for the money no matter how little or big the amount is.
"Of course if we can get more I would like it, but we have established an excellent relationship with Bangor."
But he says there is more to the teacher-training partnership than just money. "We also get some new ideas and have the satisfaction of helping teachers in their training. I'm coming to the end of my career and it's a choice: are we going to do something to sustain standards? Or complain that schools are full of bad teachers?" he said.
"If you want to influence teacher training you need to be on the shop floor working with them and passing on the fruits of your own experience."
Mr Williams joined the school as headteacher in 1998 and quickly signed up to Bangor's initial teacher-training partnership. He has trained the other teachers, who work with between three and four students at the school during the academic year.
"It's such a contrast with when I was at college in the 1960s," said Mr Williams.
"Then you were placed in a school and just taught for the whole time without receiving any advice.
"Now we don't throw them in and run away like that, we're there with them, passing on advice, it's a dialogue."