The judge said he didn't want to go into the reasons for his decision.
Two brothers aged 16, who cannot be named because they are too young, have denied murdering 10-year-old Damilola.
They also deny charges of manslaughter and assault with intent to rob.
Damilola died in November 2000 from a thigh injury caused by a broken bottle on the North Peckham Estate, south London, where he lived.
On Wednesday, the jury heard from an expert witness who said Damilola was deliberately stabbed in the thigh in a cutting and twisting motion.
Last week the court heard the evidence of a surgeon who said he thought Damilola died accidentally after falling on broken glass.
The trial, which began in January, is now in its closing stages.