This week's Living Torah talks about how the Rebbe opposed the whole world method of Hebrew instruction for children. He said instead to teach each letter with its vowels. He said this is the traditional method and it fosters emunah.
Something worse than the whole world method takes place today. It's the whole sentence method. When a school for baalei teshuva doesn't teach Hebrew grammar, the student learns whole sentences at a time. The rebbe reads an entire sentence and translates. Usually, he reads the Hebrew so fast the student can't even make out the words. He learns whole sentences at a time.
You have to teach Hebrew grammar, at least once a week.