A CTLR TRAINEE WITH AN INSTRUCTOR CLBS A SBOUND ACR THROUGH AN OPPOSITE DIRECTION ACR'S ALT. THE TRAINEE ISSUED TURNS TO BOTH ACFT; BUT THEY WERE NOT SUFFICIENT ENOUGH OR TIMELY ENOUGH TO PREVENT A LOSS OF SEPARATION.

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ACR X HANDED OFF TO ZDC FROM ZNY CLBING TO FL240. I WAS GIVING OJT TO A TRAINEE WITH APPROX 100 HRS ON THIS POS. TRAINEE CLBED ACR X TO FL310 INITIALLY THEN AMENDED TO FL280. ACR Y WAS NBOUND DIRECT TO JFK AT FL250. I WAS AWARE OF BOTH ACFT AND POTENTIAL CONFLICT BUT DECIDED TO WAIT TO LET TRAINEE RESOLVE (ACFT WOULD PASS APPROX 4 MI). TRAINEE ATTEMPTED TO TURN ACR X 20 DEGS W -- THIS WAS NOT ACKNOWLEDGED ON FIRST CALL. TRAINEE REPEATED INSTRUCTION TO ACR X THEN TURNED ACR Y 30 DEGS E. WHEN TRAINEE REALIZED THERE WOULD BE POSSIBLE LOSS OF APPROVED SEPARATION TURNED ACR X AN ADDITIONAL 30 DEGS R. COULD HAVE POSSIBLY MAINTAINED APPROVED SEPARATION WITH AN IMMEDIATE TURN AND DSCNT BUT I FELT THE DANGERS TO PAX AND CREW IN THE MANEUVER WAS FAR WORSE THAN LACKING 1 MI OF SEPARATION. SUPPLEMENTAL INFO FROM ACN 390210: ACFT SBOUND ON J79 TO VILLS INTXN. SBOUND PASSED FIRST 2 NBOUND ACFT AND WAS THEN ISSUED A CLB. THIRD ACFT CAME WITHIN 3 NM AND 500 FT OF SBOUND TFC. THIRD ACFT WAS /A EQUIPPED. HAD THE THIRD ACFT HAD RNAV HE MAY NOT HAVE TRACKED W OF THE FIRST TWO.