Emma Kimilainen set the best time of the day in W Series practice at Assen, as Sarah Moore ended FP2 fastest.
Moore set a time of 1m34.247s in the closing minutes of the late afternoon session, marking the first time she has been fastest in any W Series session this year - although that effort was not fast enough to beat Kimilainen's morning time of 1m34.195s.
Kimilainen had also set the initial pace in the second session, but was quickly deposed as a flurry of improvements from drivers including Norisring winner Marta Garcia, Gosia Rdest and Vicky Piria came in.
Alice Powell then set a benchmark time of 1m34.896s and occupied the top spot on the timesheets for the majority of the 45 minutes, before she was eclipsed once by Piria, who in turn was beaten by Moore.
Points leader Jamie Chadwick ended the second session in third place to improve on her morning performance of sixth, ultimately beating Powell who was fourth.
Jessica Hawkins continued to impress and ended the day in fifth, although she had been second in the morning session.
Kimilainen, who was unchallenged throughout the morning session, ended her Friday with a time fast enough for sixth.
Rdest was seventh, ahead of Miki Koyama in eighth and Misano podium finisher Fabienne Wohlwend in ninth.
The top 10 was completed by Tasmin Pepper.
Title challenger Beitske Visser dropped back through the order in the second session, having set a time fast enough for fourth in the morning session, and was 12th.
Despite initially having the pace to challenge for the fastest time, Garcia was 14th - dropping a further two spots back from her earlier placing of 12th.
Megan Gilkes, who was dropped back from a full-time role to a reserve position last time out at the Norisring, is back on the grid and will contest this weekend as normal. She finished 17th in FP1 and last in FP2.
Official reserve drivers Vivien Keszthelyi and Sarah Bovy also participated in both practice sessions, with Bovy's best lap time coming in FP2 with 17th and Keszthelyi finishing 19th in both.