iPhone users have an unfair advantage in test prep. The App Store's best habit and study apps are polished to a shine, and if streak tracking keeps you honest, here's the stack I'd build.
Duolingo is still the streak mechanic everyone else copies. Open it daily or watch your streak burn, and that small anxiety produces real consistency. Anki's iOS app is the premium feeling version of the best memorization tool ever made, perfect for drilling the academic collocations that IELTS and TOEFL reward. Quizlet on iOS is smooth and fast, with shared test prep sets and games that make vocabulary review feel less like homework.
Notion on iOS is where your plan lives. Build a simple tracker: daily tasks, section scores from practice tests, a countdown widget to test day. Checking boxes in Notion scratches the same itch as a streak, except it's for real study milestones instead of app opens. Pair it with Apple Reminders or Google Calendar so your study blocks appear where you can't ignore them.
Now the warning, because this matters more than the app list. Mobile app streak tracking for test prep optimizes for opening the app, not for raising your score. A 200 day Duolingo streak with zero practice tests is a very consistent way to stay at band 6.0. Streaks are the engine. You still need a driver deciding where the car goes. Track your mock test scores next to your streaks, and if the scores aren't moving, the streak is lying to you.
The 8-week study plan at internationalstudyhelp.fyi is that driver: daily tasks plus biweekly mocks, built around your target score.