Making the rounds of several high school graduation parties a few weeks ago, I was struck by something that perplexed, but did not surprise, me.

Toddlers, tweens, teenagers, parents and grandparents milled about at the various parties, congratulating the recent graduate and his friends. Cards and gifts were stacked on multiple tables and food was plentiful. On a humid North Texas evening, drinks of all flavors were iced and readily available.

At a couple of those festivities, I noticed a stream of recent graduates heading confidently to a frozen margarita machine, plastic cups in their hands; most had gotten the permission of their parents, who were at the party, to pull the lever after promising the adults they would not drive.

Was this the first time they had had a margarita, or a beer, or sang, “Jose Cuervo, you are a friend of mine” while doing shots? Who knows?

But the scenario did point to the findings in a national study released last week that quantifies, sadly, what many of us already know: many of the underage drinkers in this country have readily gotten alcohol from their parents, relatives and other adults.

For many parents, the excuse many times is that they know their children will be drinking when they are out with friends, so they would rather monitor it from their home and ensure that the youths don’t drink and drive.

There are a few problems with that: First, it’s against the law and, second, the ramifications and consequences of introducing alcohol to young adults could lead to dependence or abuse, binge drinking, driving while intoxicated and traffic-related deaths, among others.

Last week the Substance Abuse and Mental Health Services Administration released a study — based on data of 158,000 youth between 2002 and 2006 compiled by the Surveys on Drug Use and Health — that gave us details about teenagers and alcohol.

Among its findings:

“40 percent of the underage drinkers said they got alcohol from an adult in the last 30 days.

“50 percent of the underage drinkers got their last alcoholic drink at someone else’s home.

“30 percent got their last drink at home.

“3.5 million young people each year meet the qualifications of having an alcohol disorder.

“5,000 teens die in alcohol-related incidents each year.

“In far too many instances parents directly enable their children’s underage drinking — in essence encouraging them to risk their health and wellbeing,” Acting Surgeon General Dr. Steven K. Galson said. “Proper parental guidance alone may not be the complete solution to this devastating public health problem — but it is a critical part.”

The study also said that rates of underage drinking were higher in the Midwest and Northeast. In one recent case, a parent and her twin children in Nassau County, N.Y., were charged under that state’s social host law by making alcohol available to minors.

Police responding to 911 calls had found more than 200 young people at their home and with beer and other alcohol being served, according to a report in Newsday. One of the scenes police described was that of a girl — “vomiting and struggling to stand” — who said she had taken six vodka shots within an hour.

Just imagine if this girl had gotten behind the wheel of a car if police had not arrived.

Last week I became concerned when my 15-year-old namesake missed one of his driver’s-ed classes because of scheduling conflicts during a hectic summer day.

Telling me he would get it rescheduled on a Saturday morning, his friend Alexander, who had taken the same course a year earlier, quickly piped in.

“Uh, don’t worry, sir, all they really do after the first class is to tell you not to drink and drive,” he said, hinting that the driver’s-ed curriculum had most likely changed in the decades since I learned to drive.

At the time, I was concerned that maybe we were paying too much to an outfit for not actually teaching “driver’s ed,” but, at the same time, I also was content that others were drilling into our son, as we had done with his older sister, the dangers of drinking, and of drinking and driving.

So as we head into the three-day July 4 weekend, let’s raise a toast to our Founding Fathers, but let’s be sure to remind our country’s youth that they can find Samuel Adams’ greatest contribution to our country on the bookshelf, not in the refrigerator.