Good eye contact, a firm handshake and self confidence can pave the way to a good interview. Turns out, that's the case even if the applicant is 4 or 5 years old.

In the frenzy to get kindergarteners into the top private schools, parents are now hiring consultants to coach their children on the art of the interview.

Dana Haddad conducts a mock interview with a group of young clients. Alfred Giancarli for The Wall Street Journal

For years, such preparations have been the norm for the standardized tests children must take to get into private schools, the so-called ERBs, which measure IQ and are administered by the Educational Records Bureau. But after a cottage industry devoted to test-prep materials and classes developed, parents say scoring in the top percentile or two became the norm rather than the exception; schools such as Horace Mann, Dalton and Collegiate began placing more emphasis on the interview and getting more granular in their assessments.

Since New York parents have a tendency to exaggerate their sons' and daughters' piano or French skills, admissions directors say they like to see any special talents with their own eyes.

"Scores on the ERBs went up because kids were preparing and parents began thinking, 'My kid got a 99 but so did my neighbor's kids, what else can we do to better our chances in this market?' " says Suzanne Rheault, a 40-year-old mother of two who left Wall Street last year to start New York test-prep company, Aristotle Circle.

Enter the mock playdate.

On a recent morning in Manhattan, former Horace Mann admissions director Dana Haddad asked a group of 4- and 5-year-olds: "Do you have your marching shoes on?" The children began marching, left their parents behind and followed after Ms. Haddad, as she led them into a Midtown office turned preschool playroom, the new headquarters of Aristotle Circle.

As the children followed tasks such as identifying their name tags, putting together a puzzle or drawing a series of shapes, Ms. Haddad and two educational consultants took copious notes.

One 4-year-old "appeared slightly shy at the beginning of the playgroup," requiring the moderator "to occasionally need to repeat a question," read a six-page assessment provided to her parents within a few days of the playgroup.

How to Practice for the Private-School Playdate For tips on how parents can help their children ace their playdate, Metropolis spoke with Murr LeBey, a private admissions adviser at Blue Tomato in New York. Here's what she had to say.

The assessment concluded that the child "appeared to enjoy the game of 'Simon Says,' engaging in gross motor tasks such as jumping, clapping, hopping" but other skills were "more challenging, such as balancing on one foot (she was not fully able to balance for more than 1 second or so)."

Accompanying the assessment is suggested activities for improvement such as encouraging the 4-year-old to speak directly with a waiter to place her own restaurant order or handing the money to the cashier at the grocery store to emphasize more natural interaction with adults.

"You're trying to be that peacock, to be noticed and it's a lot of work and a lot of pressure," says the girl's mother, who only identified herself as Ellen. She declined to provide her last name for fear of retribution from the schools where her daughter is applying.

"While you can't just prep all the time, the report and suggestions help me focus and I'm OK with that," she says.

Like most things in New York, the sessions don't come cheap. Aristotle Circle charges $400 for a 45-minute observation and assessment. Bright Kids NYC, a similar company started last year by Bige Doruk, a mother of three, charges between $175 to $275 for sessions lasting between 45 and 75 minutes.

"They call it a playdate," Ms. Doruk says. "We call it just another test to prepare for."

In New York City, getting into some private schools is akin to getting into Harvard. Come September, Horace Mann has only 35 spots and will likely receive hundreds of applications (Harvard's acceptance rate was 6.9% for the class of 2014). The admissions procedure generally requires parents to submit an application and school records, attend a tour and interview with admissions officials. Children generally are required to take an ERB-administered test, visit the school and participate in an interview or playgroup.

ERB's president, David Clune, says more test-preparation services haven't led to dramatically increased scores.

Admissions consultants say more weight is being put on the interview-observed play time— to help spot the best among high scorers. During the playgroups, children are tested on dozens of areas including fine motor skills and the ability to follow directions, as well as quirky measures like how they hold a pencil, if they make eye contact with adults, or whether or not they can pour their own juice.

"You're watched from the moment you enter the door," Ms. Haddad says. "We note everything—from whether or not the children can separate easily from their parents or recognize which name tag belongs to them." Too much preparation can backfire.

Ms. Haddad tells stories of children explaining to admissions directors that their parents promised them ice cream for good behavior during the interview. Others have blurted out that they've already been preparing for play dates. "Admissions directors don't like that," she says.

Write to Shelly Banjo at shelly.banjo@wsj.com