I have mixed feelings about what my little guy, just shy of three years old, is really doing in “school.” Picking him up some days, I watch him rip around the yard climbing and screeching down the slide, his tiny face covered in rainbow paint, body crusted with clay, shoes and pants on backwards and it looks like controlled chaos – fun and social, but really – it’s preschool.

Other days I’m stunned at the sophistication and creativity I see in his picture reports and recounts of the day’s activities and group discussions. The idea that my little curly-haired garbage-truck enthusiast is contributing to a thoughtful discourse on rainbows or how turtles grow makes my heart skip. His brain is in the throes of the most breathtakingly rapid growth of his life. I know his time at home and relationship with me and my husband is number one, but just behind that in influence are the hours every day that he spends building, flexing his fledgling critical thinking skills, and yes, burrowing in clay at preschool.

But not all preschool programs are created equal. The good news is that research on which skills are important and how to build them is pretty consistent and growing. The bad news, though, is that many schools aren’t set up around promoting those very skills. Why the gap? And how can you tell if your kid’s preschool is kick-starting the right mental strengths?

A recent early education study found that kids who are in preschool for two full years get further ahead in certain academic skills than kids who only attend one year before kindergarten. The kids in the study who entered preschool at age three had significantly better “decoding” skills (the ability to break words down into component sounds) and letter knowledge by the time they were four than did their same-age peers just entering year one. And the effect was additive – both groups developed during the second year of school, but the ones who had entered at three stayed consistently further ahead.

These early literacy skills are strong predictors of later reading proficiency, and the results fall in line well with previous studies that show high quality preschool programs (with trained, decently paid teachers and relatively low student-teacher ratios) give kids, especially ones from lower socioeconomic backgrounds, a boost in early academics.

That sounds pretty good, but another outcome of the study was perhaps more telling; the research showed, as others before it have, that preschool programs did not help kids with arguably the most important skill needed for success in life: self-regulation.

Self-regulation means the ability to plan, control impulses, focus, and keep multiple pieces of information in your head at once (called “working memory”). Sounds like a daunting task for a fast-moving, inherently bipolar little preschool creature, but, in fact, the brain regions that affect self-regulation connect and strengthen quickly in the second and third year of life. The prefrontal cortex and its pathways to memory regions like the hippocampus, and emotional centers like the amygdala allow even the smallest kids to begin holding and integrating information to make plans and have broader mental pictures.

The recent book NutureShock cites a growing body of research that shows self-regulation trumping all other skills when it comes to achievement. For example, kids in the national “Tools of the Mind” preschool program, which focuses on building self-regulation, drastically outperform other children on measures of behavior, emotional skill, and academic abilities. Children in these classes have been shown to be a full year ahead on national standardized tests, and early on when they were randomly assigned, kids came out measuring significantly higher than control groups in most areas, like vocabulary, math abilities, and even IQ.

So if self-regulation is so important, why do studies show that most preschool programs don’t help kids with this skill at all?

In short, our traditional view of self-regulation is outdated.

Take the recent preschool study cited at the beginning of this essay; in it, the researchers define self-regulation practice to be when teachers make kids “follow directions and classroom routines, pay attention, stand in line, and sit properly.” Whether a kid can wait in line and follow directions may be a decent measure of one aspect of self-regulation (impulse control), but it doesn’t help that child build the highly complex self-regulation skill set (involving working memory, planning, and so on).

The true exercise of self-regulation comes more in the form of imaginary play, following a genuine curiosity, planning an activity around it, and focusing on it for an extended time. When people say kids in school don’t “play” enough, it’s true, but productive playing isn’t just running aimlessly from one thing to the next whenever the mood strikes. Preschool programs that ask kids to express an interest, use imagination (since this taps the cortex’s capacity for abstract thought), plan ahead, and keep checking in with themselves to see how the plan is going – this is when research finds positive results for outcomes years down the line. The old-school notion of self-control means sit properly in your chair and don’t bite your friend, but the science-backed notion has more to do with planning and executing a game of make-believe fire station.

Come to think of it, when I picked my son up earlier this week, he and three other kids were sitting in the sandbox with colanders on their heads, playing a game of their creation: “pirates and chefs.” I laughed and had one of those “it’s just preschool” moments. But the teacher remarked that they had designed the game and had been at it for 30 minutes already, each with their serious roles. Now when I think about it, I realize that’s not just fun and entertainment for my little preschooler – that’s him flexing one of the most critical, brain-building skill sets he’ll need for decades to come.