Does anyone recall this movie?

Factual Questions
1

My sister and I were talking about it yesterday and would like to see it again, but we can’t remember the name.

It is an early 80’s film about a school for mentally challenged/autistic children. Details I recall are a child who would speak incredibly fast(faster than the Micro Machines guy) and when recorded onto tape and slowed down was shown to be speaking like a television game show host.

Also they would sing a song that goes:

Dig dig do do
Dig dig do
Dig Dig do do
Dig dig do

Diggy diggy do
Diggy do do
Diggy diggy do
Diggy do do

2

I suspect that it was this 1977 made-for-TV movie, A Circle of Children with Jane Alexander. There was also a sequel a couple of years later.