Why Isn't My Child Reaching His Milestones?

When my daughter Rachel was 13 months old, I decided to enroll her in a movement class. I reluctantly placed her in the "crawlers" group; at her age, I was positive she'd start walking any day. Four months later, she was still happily crawling on the foam mats, and I was in a panic: Seventeen months and still not walking? What was wrong?

A mere month later, Rachel sprang up on her feet, and today -- seven years later -- she ice-skates and dances ballet with skill and grace. When it came to walking, she was a typical late bloomer, a child who is developing normally, but achieves a milestone or two at the later end of the spectrum. Experts say that developmental leaps, such as learning to walk, take place only after numerous supporting skills have come together, and the rate at which those pieces assemble varies among children.

Of course, sometimes slow development indicates a condition that requires treatment. Here's how to tell if your baby is merely a late bloomer or if he needs some outside help.

Crawling and walking are two eagerly anticipated milestones; there's nothing like the thrill of watching your baby zoom across the room to claim his favorite toy -- or your cell phone. Experts say that babies usually begin crawling at 7 to 8 months, walk with support at 9 to 11 months, and begin to walk on their own just before their first birthday.

More complicated large motor skills, such as walking up stairs and jumping, occur at 16 months and two years respectively. But here's the rub: These "typical" ages don't reflect the wide variation that occurs among perfectly normal children. In fact, according to research from the University of Missouri-Columbia, 90 percent of babies crawl between the ages of 5 and 11 months, walk alone between 9 and 17 months, and jump with two feet between 17 and 30 months.

Why such variation? One reason is muscle tone. Babies whose muscles are a little weaker than average may be slower to walk, as may chubbier babies. "Weight distribution also plays a role," says Joseph Campos, PhD, professor of psychology at the University of California, Berkeley. "A top-heavy baby needs to develop extra strength to keep his balance."

Practice time can affect motor development as well. For example, a study by British researchers at the University of Bristol in the 1990s found that 6-month-olds who were put to sleep on their back had lower gross motor scores than 6-month-olds who slept on their front. (The difference disappeared by the time the babies reached 18 months.) The reason seems to be that the back-sleepers didn't have as much opportunity to strengthen their neck and shoulder muscles as the front-sleepers did.

While the American Academy of Pediatrics strongly advises parents to put their babies to sleep on their back as a way of minimizing the risk for sudden infant death syndrome (SIDS), many pediatricians are urging parents to place their baby on their tummy periodically during playtime to help them build their upper body.

Finally, temperament can influence motor development. According to a study by Campos and his colleagues, babies who were prone to frustration began walking two to four weeks earlier than other babies. "Temperamentally, these babies were inclined to find a faster and more efficient way than crawling to get to where they wanted to be," says Campos.

When motor delays fall outside the normal ranges, children can often be helped with some type of treatment. If the delay is caused by low muscle tone, for example, a course of physical therapy can help build strength and fine-tune coordination. "Sometimes we give the child a walker to help him take steps. Over time, we take it away as he is able to bear more weight on his feet," says Lori Freedman, an early-childhood developmental specialist in private practice in Edgemont, New York.

Rebecca Luckenbach, a Cincinnati mom, recalls that her son, Gavin, was diagnosed with low muscle tone as an infant because he wasn't meeting his large motor skill milestones. "The therapist would show us exercises for him," she recalls. "For instance, we would press our hands against his hands and feet to encourage him to push back."

Sometimes motor delays are a sign of more serious genetic or neurological disorders, such as cerebral palsy (a brain disorder that can be characterized by spastic movements). If your child's motor development seems extremely delayed, consult your pediatrician.