The article is correct, many students do begin school very far behind their peers - research shows it to be true, and the teachers on the board know this. If there is little conversation at home, if no one reads to the children, if they haven't learned colors or numbers or associated the written word with the spoken word before they begin school, they will certainly be far behind.
Intervention in the home would certainly be preferable, if you could come up with an intervention program that would be effective with teenaged single mothers who are likely uneducated and put little value on education themselves. (Add in the likelihood of substance abuse in the home, and where do you go?)
I know that in some states, such intervention programs exist and serve children and families from birth, but they are voluntary. A young woman of my acquaintance has participated in such a program, but she & her husband are college-educated and would have read to and educated their toddlers at home even without such a program. Do the parents who really need the program, and for whom it is designed, participate? I don't know.
Interesting point. We do have a program around here called “Parents as Teachers.” The only person I know to have participated is a fourth grade teacher and her husband. Having P.A.T. available to pregnant teenagers would probably be more effective than head start. Depending on how it is arranged, it could be done at a much lower cost, especially if the school has onsite daycare.