Having worked for two airlines (Including QF) as cabin crew I can vouch for it.
Some exams you need 100% pass rate, most you need over 80%. Rocking up late is seen as a reflection of your reliability so if you're late without a valid reason they look into it. Ground School is usually sorta boring to be honest, a lot of study and concepts to wrap your head around if you've never worked in the industry before I guess.
Im currently studying to be a pilot full time doing my multi rating and found Ground School for QF more intense. Also make sure you can swim, two blokes from my intake got dropped because they couldn't swim fully clothed for 100m and tread water :P
Tips would be- study, sleep, study and sleep during training. Don't get involved in all the pointless drama that seems to be imbedded in cabin crew life. Don't let passengers talk to you like crap when you start flying and don't eat too many crew meals unless you want to explain to your base manager why you're ordering a larger uniform set 3 months after you started.
Good luck man.