Lots of past posts on this on 'Security Matters' and 'Home Phone' forums with various suggestions for workarounds and remedial measures.
As you have spotted it was a scam call. There is no point in reporting it to anyone (unless you have actually been a victim of crime) as it won't reduce any future scam call attempts against you.
Little point in blocking numbers either as these are either faked, or a cloned real number from an innocent party, and will change for each call so any number you block will most-likely never be used again and the number block will never be applied.
Personally I wouldn't leave any remote access software installed on my computer. If your grandson needs to receive legitimate support on a computer from a verifiable source then the standalone 'Quick Support' option for Team Viewer is better IMO. It can be run once and deleted after use. His school may, however, have its own requirements and processes in place.
Screening the scam calls is a better approach IMO. Search the VM forums for trueCall for lots of info on this call screening device or a BT phone which has trueCall features built in.