THE LAST TIME I intervened after a father struck his child in public was on the line waiting for the Swan Boats in the Public Garden last summer. A well-dressed man a few inches taller and 25 years younger than I swatted his fretting 4-year-old daughter hard on the buttocks. As in Elissa Ely's column (''Up in the air,'' op ed, July 26), the girl's mother appeared to ignore both what he did and the child's reaction.

I went up to the father and told him that I was a doctor and said in a kind voice that I could see that he was having a hard time waiting in line with his daughter. I added that there was never any need to hit a child, that hitting her was neither going to help control her behavior nor improve her relationship with him. My tone of voice was warm, calm, and confident.

The fellow looked at me, seemingly amazed, and responded in a Southern accent to the effect ''Really?'' to which the mother, embarrassed, added ''We really don't do this very much.''

To my knowledge there is no science behind Ely's comment that ''given ugly human nature [to accuse him of public violence] would make him more likely to punish his son in private.''

Experience and research, my own and those of others, indicate that taking action against abuse, bullying, and sexual offenses effectively deters recidivism.

See Chapter 6 - "Discipline and Punishment" from Dr. Newberger's The Men They Will Become, and his letter to The New York Times about Baumrind's flawed study, August 27, 2001

All adults, and especially those of us in the helping professions, should learn how to step out of the bystander role in protecting children.

When we see children being hurt, we need to intervene in a clear and kindly way.

ELI H. NEWBERGER

This story ran on page A18 of the Boston Globe on 8/1/2002.