aged 1.9 to 2.4 was the terrible period of my son :-( . He went to pre-K from aged 2.6, his condition has improved from aged 2.9. It was very good from then to 3.7. Now, he is aged 3.9, his bad temper has come again!!!!! However, it is not as terrible or horrible as before. I think aged 1.9 to 2.6 is the black period of kids