Baxter!

Baxter! is a 1973 drama film directed by Lionel Jeffries and starring Patricia Neal, Jean-Pierre Cassel and Britt Ekland. The film follows a young boy called Roger Baxter who struggles to overcome his speech problem (rhotacism) and his strained relationship with his parents. The screenplay was by Reginald Rose, based on the 1968 book by Kin Platt, The Boy Who Could Make Himself Disappear.

Synopsis from Wikipedia, CC BY-SA 4.0. Everything below written here.