They say your child is a late-bloomer? Be patient, and take heart!

I was dragging my feet when I walked into my son's school that afternoon. ''I'd like to talk to you,'' his sixth-grade teacher, Mrs. Green, had written in a note sent home. To talk about my son's problems, my heart told me. Those poor report cards. That lack of interest in his studies. His indifference to challenge.

Prepared for the worst, I tensed when Mrs. Green started to speak.

''I know you're worried,'' she began, ''after all those achievement tests showing your son's ability, his high IQ. I would have been worried, too, when I first started teaching years ago.

''By now,'' she went on, ''I've learned to love dreamy boys like your son, who take so long to see it is important they work hard in school. These are the ones educators call late bloomers. Sometimes they are out of school, and young or even older adults, before they do what I call 'catch fire.' ''

Seeing my puzzled look, she added, ''It's a concept hard to grasp, and it's especially hard to find the necessary patience to deal with it.''

Me, find patience, when I was so concerned about our son? I stifled a groan. Still, I'd always been aware of what Mrs. Green was saying: Some people grow up faster, come to maturity later than others. And yes, I knew you can set a date with your children to have a picnic, or go to the zoo, but you cannot set a date when maturity will come. Nor can you force it to come. As for late bloomers, I'd heard the term, but I'd lost sight of it.

So what did this mean? Simply that my husband and I were apparently going to have to wait - and wait - for our son to meet the expectations his abilities pointed him toward, until in the course of time he would cease being an underachiever and find his niche in life.

Returning to my car in the school parking lot, I sat quietly behind the wheel before starting the motor. Patience, where are you? Yet I was already encouraged. Mrs. Green had given me guidelines explaining what she believed are some of the current influences on late bloomers (more likely to be boys than girls, she said).

For instance, some youngsters are held back by fear - fear of all the achievement tests they have to take nowadays, the acceleration offered them, the tough, in-depth classwork of modern education. They fear failure.

Or take indecision. Career choice often nags at youngsters early, since there are so many specialties in all fields today.

Then there is the lack of motivation. Without motivation, ability and preparation are of little use. Take the brother, challenged by a sister's good grades and achievements, who was supermotivated to keep up with her, and as a result reached heights once thought impossible for him.

The maturity of discipline is of special importance to late bloomers. In the school years, extracurricular activities, social life, and athletics often scramble the educational process. Mrs. Green had said, ''I tell my students that without self-discipline they cannot go far. I believe I have helped some to set reasonable priorities. Others come to this much later in life.''

As I started the car, I realized I was already viewing my late-bloomer son with more good feelings than in a long time. So he had a future after all!