The early pieces seem to be coming together for BASIS, the Arizona-based charter school group that promises an unprecedented level of rigor when it opens its D.C. campus this summer for grades 5 to 8. It has a building in Penn Quarter, and 319 students who registered during an open enrollment period that ended Friday. That’s short of the 400 that officials targeted, but head of school Mary Riner Siddall said the good news is that no lottery will be necessary.

“I am very happy about this fact that we won’t have to let anyone down,” she said in an e-mail. She held more than 30 informational sessions all over the city for prospective parents. Registrants represent more than 75 schools across all eight wards, she said.

When BASIS founders Olga and Michael Block announced plans to come to D.C. last year, their calling card was an uncompromising European-style academic program. Seventh graders would take Algebra 1 and Latin. There would be nine hours a week of physics, chemistry and biology. To graduate, students would be required to complete at least eight AP courses and pass six exams. Eighth graders will have to pass the University of Cambridge international benchmarking exam. It was a formula that earned their Arizona schools national ranking and test scores that exceeded statewide averages.

Skeptics pointed out that it was also done with a student population far less diverse than the one it would encounter in D.C. The Blocks brushed aside such concerns.

“We know how to do this,” said Olga Block. “We’re very good at it.”

But it turns out that BASIS will in fact be making some modifications to its rigorous program, tweaks that Siddall calls temporary but necessary.

Siddall said all students will still take the six AP exams, including AP calculus, before graduation. But in 2012-13 only, BASIS D.C. will modify its 7th and 8th grade curriculum, separating math courses into different levels “to account for the fact that not all 7th graders are ready for Algebra 1 and 8th graders Algebra 2...They will still get the same physics, chemistry, biology 9 hr/week, it will just not be as deep.”

She rejected the idea that D.C. students will be getting BASIS lite.

“Not a watering down, just a willingness to meet kids where they’ve been,” she said, adding that other new BASIS schools started out the same way.

To help new students close academic gaps before school starts, BASIS is offering its STARS program, three hours per week of small group tutoring in reading, math and study skills.