We have a house rule for the Littlest Scholar -- she can use mom's computer for an hour to play games. She may use my laptop too, but only for schoolwork or to use Microsoft Office, which Mrs. doesn't have. She used Office the other night to make a Christmas list for Santa, replete with graphs indicating her satisfaction with gifts received from parents and Santa. (We did not measure up.)

LS has asked a few times for her own computer, and I've thought it would not be a good thing because she already spends too much time in front of screens and too little time in front of the printed page. I now have my supporting documentation.

For all the schools and parents who have together invested billions to give children a learning edge through the latest computer technology, a mammoth new study by German researchers brings some sobering news: Too much exposure to computers might spell trouble for the developing mind.

From a sample of 175,000 15-year-old students in 31 countries, researchers at the University of Munich announced in November that performance in math and reading had suffered significantly among students who have more than one computer at home. And while students seemed to benefit from limited use of computers at school, those who used them several times per week at school saw their academic performance decline significantly as well.

"It seems if you overuse computers and trade them for other [types of] teaching, it actually harms the student," says lead researcher Ludger Woessmann in a telephone interview from Munich. "At least we should be cautious in stating that increasing [access to] computers in the home and school will improve students' math and reading performance."

There is a longstanding joke on college campuses about professors who seem to constantly show videos, wheeling A/V equipment in and out of their classrooms because they haven't anything useful themselves to say. In economics, we say that if you add one input and hold all others constant, you get diminishing returns -- and what they forget to tell you is that if you keep doing it, returns become negative (this is the "third stage of production"). If teachers don't add other inputs to the increasing use of computers in the classroom, where does the third stage kick in?