2 PA28'S AND A BE55 FROM THE SAME FLT SCHOOL DEPARTED AN ARPT VFR FOR XCOUNTRIES TO THE SAME DEST AND INADVERTENTLY ENTERED IMC PRIOR TO GETTING THEIR IFR CLRNCS.

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FILED AN IFR FLT PLAN FROM ZZZ TO ZZZ1. PROCEEDED TO TAKE OFF FROM THE RWY; BEING THE FIRST ACFT IN A FLT OF 3 CONSISTING OF ANOTHER PA28A AND A BARON 58 ALL WITH THE SAME DEST. CFII FIRST TRIED TO ESTABLISH COM WITH CTR WHICH FAILED THEN TRIED FSS AND FINALLY APCH. UNABLE TO ESTABLISH COMS WITH CTR AND FSS; HE WAS ABLE TO REACH APCH AND ASKED FOR OUR CLRNC. HOWEVER; BY THIS TIME THE WX HAD DETERIORATED AND WE WERE NO LONGER ABLE TO MAINTAIN VFR. I CONSIDERED MAKING A 180 DEG TURN OUT OF THE CLOUDS BUT I DID NOT KNOW WHERE THE 2 ACFT THAT HAD TAKEN OFF BEHIND US WERE AND I DID NOT WANT TO RISK A MIDAIR COLLISION. ALSO; THE CFII WHO WAS WITH ME IN THE AIRPLANE AND HANDLING THE RADIO CALLS DID NOT SEEM CONCERNED. THE CFII THEN CONTACTED APCH ASKING FOR OUR CLRNC. APCH THEN INSTRUCTED US TO MAINTAIN VFR. WE REPLIED THAT WE WERE UNABLE TO DO SO. APCH THEN ASKED IF WE HAD ENTERED IFR CONDITIONS WITHOUT AN IFR CLRNC. WE REPLIED THAT WE HAD. WE THEN RECEIVED OUR CLRNC. THEN THE CTLR ASKED IF THERE WAS A CFI ON BOARD TO WHICH THE CFI SAID 'YES.' THE CTLR THEN TOLD HIM TO CONTACT THE TWR AFTER WE LANDED. WE THEN CONTINUED ON OUR RTE WITHOUT FURTHER TROUBLE.