JUDY WOODRUFF: Next: How much emphasis should we put on reading and other subjects in the earliest years of school and preschool?

Some say that crucial development through playtime is getting lost in the shuffle for the very youngest students.

Special correspondent Cat Wise has this story for our weekly series on education, Making the Grade.

CHILD: Let's go, Liam. Let's go, Karen.

CAT WISE: At ages 3, 4, and 5, most children want to play pretend.

CHILD: This is our babies.

CAT WISE: But in today's world of high-stakes academic testing, some preschool teachers feel pressure to put away the baby dolls and pick up the school books.

GERALYN BYWATER MCLAUGHLIN, Teacher, Mission Hill School: I have been teaching for 25 years, and I have seen a big change.

So you're pretending to be the sister? And you're pretending to go on a walk?

CAT WISE: Geralyn Bywater McLaughlin teaches prekindergarten at Mission Hill, a public school in Boston.

CHILD: I'm the momma.

GERALYN BYWATER MCLAUGHLIN: So you're the momma?

CAT WISE: She and other educators have started a campaign they call Defending the Early Years.

GERALYN BYWATER MCLAUGHLIN: The goal of Defending the Early Years is to really help rally early childhood educators to push back against this push-down of academics into the early years. The standardized tests, the disappearance of play, teachers are feeling it, and we're helping to bring voice to their frustrations and their concerns.

CHILD: This is my baby.

CAT WISE: Bywater McLaughlin says education policies that tie government funding to academic performance like No Child Left Behind and Race to the Top have put pressure on preschool and kindergarten teachers to prepare students to compete in higher grades.

NANCY CARLSSON-PAIGE, Early Childhood Development Expert: The teachers feel like they're over a barrel. They have got to drill the kids on these things to get the scores so the program doesn't lose funds.

CAT WISE: Nancy Carlsson-Paige is a professor emerita at Lesley University and author of "Taking Back Childhood."

NANCY CARLSSON-PAIGE: There's been a snowball that's been rolling for 15 or 16 years. It's propelled by a belief that you will improve education and close the achievement gap if you have accountability, if you have more testing.

CAT WISE: Carlsson-Paige points to new expectations for children to read in kindergarten.

What's the harm in getting a kindergartner to learn to read? I mean, is there a harm?

NANCY CARLSSON-PAIGE: There is an absolute harm. It's harmful because you're forcing children to learn things that are out of step with where they are developmentally. And you're doing it in a way that it contradicts how they learn.

CAT WISE: Advocates of Defending the Early Years say young children do best in schools that emphasize play and project-based learning, like Mission Hill Elementary, a pilot school.

JADA BROWN, Teacher, Mission Hill School: So, the cabinet is for what?

CAT WISE: Here, desks are replaced by project areas, where kindergarten teacher Jada Brown says young students can pursue interests at their own pace.

JADA BROWN: Our school is really focused on trying to make sure that kids are engaged in activities that they are choosing, that they're interested in, and that it's not the adults who are pushing particular things on them.

CHILD: We could use this for measurements.

JADA BROWN: We could use that for measurements.

CAT WISE: On this day, kindergartners built cabinets for a pretend kitchen, and learned some math while doing it.

CHILD: We're putting a math thing over there, because Josie is trying to help me with my math.

JADA BROWN: What kind of math?

There's so much math that actually happens in building. How do you build a structure? How do you make sure that it's standing? It's all math. It's science. It's trying to figure out, how do you make something that's stable.

NANCY CARLSSON-PAIGE: The fact of the matter is, play and learning are the same thing with young children.

CHILD: Josie, I need a few sticks for this.

CAT WISE: How do you respond to those that say, but kids are coming to school to learn, they should be writing their ABCs, and they can play at home?

JADA BROWN: The home looks very different from school. There is a lot that's going on in that classroom, whether it's art or math. The materials that are in the classroom are a lot different from what you might see at home.

CAT WISE: Ayla Gavins is the principal of Mission Hill.

AYLA GAVINS, Principal, Mission Hill School: For us, the skills are not taught in isolation, but they're taught embedded in some sort of meaningful work or exercise. I believe they learn more because they're motivated.

BILLYE TOUSSAINT, Parent, Mission Hill School: What do you think, Ayanna?

CAT WISE: Parent Billye Toussaint's daughter attends preschool at Mission Hill.

BILLYE TOUSSAINT: One of the things I really, really wanted my own children to have is this ability to not always need an adult, like, pushing, pushing, pushing, and able to really take control of their own learning.

MAN: You're going to go straight to your independent work.

CAT WISE: Kindergarten looks and feels a lot different at Harlem Prep, a high-performing charter school in New York City. The focus is on school work over play.

ROBERT PONDISCIO, Fellow, Thomas Fordham Institute: What is the argument that is being made here?

CAT WISE: Robert Pondiscio, a fellow at the Fordham Institute, who also teaches civics at Harlem Prep's high school, says play-based learning does benefit some children, but may not the best way to serve low-income students.

ROBERT PONDISCIO: If you are a low-income kid, you don't have the enrichment opportunities that more fortunate kids get. And that really means that you show up for school on day one further behind. So if schools are not aggressively attacking that problem from day one, those kids will not only not catch up; they will fall further behind.

CAT WISE: Pondiscio believes high expectations, like reading in kindergarten, have helped Harlem Prep students excel.

ROBERT PONDISCIO: Nobody, but nobody is going to sensibly argue that young children shouldn't spend a lot of time in pre-K and kindergarten playing. I'm not suggesting that we should be turning anybody's pre-K or kindergarten into an academic hothouse. But I worry that it could become easily an intellectual death sentence for low-income children.

Students like ours are simply not going to get that rich vocabulary, that rich background knowledge, that linguistic proficiency that other kids bring to school from home.

CAT WISE: Harlem Prep takes pride in preparing children for college at a young age; 93 percent of the students in this Democracy Prep Network go on to college, including some of the country's most elite schools.

For her part, Nancy Carlsson-Paige says the best preparation for college starts with age-appropriate teaching.

NANCY CARLSSON-PAIGE: The faulty thinking is, we will prepare kids to be college- and career-ready by drilling them on letters and numbers when they're really little, and that will get them ready for success in school. But the truth is the complete opposite.

CAT WISE: Both experts agree the final destination should be college. The issue is how to start the very young on that path.

For the "PBS NewsHour," I'm Cat Wise.