Kieran Kent pipped Calum Beach to the top spot in free practice one after clocking a 1min 46.782sec lap to give him a 0.610sec edge.
Jack Kirch ended the session third quickest and just slightly ahead of Keo Walker in fourth as Harry Cook rounded out the top five.
HEL Performance British Junior Supersport Championship with Motocourse, Donington Park, FP1:
1. Kieran Kent (D&P Lovell Kent Racing) 1min 46.782s
2. Calum Beach (UPVC Outlet Racing) +0.521s
3. Jack Kirsch (3D Racing) +0.894s
4. Keo Walker (Keo Walker Racing) +1.140s
5. Harry Cook (McAMS Yamaha Junior Team) +1.202s