I know what you mean Ultramarina! My kids almost always do better being taught by other people. Instruction from their parents just gets their backs up and quickly spirals into uselessness.

Also, if I homeschooled my DS we'd spend the day with him questioning every word I say ("Why do I need to study math? What is this 'math'? What is 'is'?" etcetera), or picking apart my grammar as I instruct him. LOL