AN INST INSTRUCTOR AND STUDENT CAUSED AN ACR B737 TO GO AROUND WHEN THE STUDENT STOPPED ON THE LNDG RWY AT ISP.

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WHILE ON A PRACTICE ILS RWY 6 APCH TO LNDG AT ISP WITH MY STUDENT UNDER SIMULATED IMC (HOODED); HE WAS ORIGINALLY CLRED FOR ILS RWY 6 CIRCLE RWY 33L. HE WAS ASKED BY ATC IF HE COULD ACCEPT A STRAIGHT-IN LNDG ON RWY 6; HOLD SHORT OF RWY 33L. THE STUDENT WAS MORE FAMILIAR WITH THE ARPT ENVIRONMENT THAN ME AND ACCEPTED THE CLRNC. WITH A HIGHER MDA ON CIRCLING THAN STRAIGHT-IN; I HAD HIM REMOVE THE HOOD EARLY TO MAKE SURE HE COULD LAND AND HOLD SHORT OF RWY 33L. THE RADIO (COM #1) MALFUNCTIONED AND WE NO LONGER WERE HEARING ATC. THE STUDENT LANDED ON RWY 6; AND WAS UNABLE TO STOP BEFORE RWY 10. NOT KNOWING IF THERE WAS AN INTERSECTING TXWY BEFORE RWY 33L; HE STOPPED ON THE RWY AND CALLED ATC FOR PERMISSION TO DO A 180 DEG TURN AND TAXI BACK TO RWY 10. AFTER GETTING NO RESPONSE; I ADJUSTED THE SQUELCH DIAL AND ATC COULD BE HEARD AGAIN. THEY ASKED US TO TAXI OFF THE RWY 6 AT TXWY B3 AND INFORMED US THAT A B737 HAD TO GO AROUND BECAUSE WE STOPPED ON THE RWY. I FEEL THAT THE SIT COULD HAVE BEEN PREVENTED IF I HAD CONSULTED THE ARPT DIAGRAM SO THAT I KNEW WHERE THE INTERSECTING TXWYS WERE SO THAT I COULD DEPART THE RWY ASAP. I WAS OVERLY CONCERNED WITH HOLDING SHORT OF RWY 33L FOR OTHER TFC UNDER LAHSO THAT I DIDN'T REALIZE THAT I WAS CREATING A CONFLICTING SIT ON RWY 6. CONTRIBUTING FACTOR WAS THE SILENCE ON THE RADIO MADE IT APPEAR THAT THERE WAS A 'SLOW' PERIOD AT THE ARPT BY THE SILENCE OF THE CTLRS.