My wife goes through this all the time.
This year (teaching third grade) 2 kids who could barely read their own name, let alone write it, can't add 1+1 etc, lots of conferences, phone calls, letters to the parents. It does NOTHING!!
If the parents are involved in their child's life, they know how they are doing in school, if they don't know, a phone call from their teacher will not change that.