Whilst there is not a standard percentage pass mark, from my limited experience, I would suggest 60 to 70% at this stage on the GL assessment papers will translate into a pass.
For what it is worth I would suggest:
1. Be realistic about scores, are they achieved under timed conditions? whilst accuracy is important, an ability to work against the clock, and at the very least to get a response marked on the answer sheet, is going to increase the chances of success. Especially in the Mathematics paper which historically has been time scarce, although my daughter refused to guess any, as she felt it was unfair if she could not explain her logic!
2. If you practise regularly over the summer holiday, I understand a 10% improvement is achievable, thus focus on what can be achieved in September, and not where you are now. However, my daughter did not want to practise over the summer as she saw the break as her holiday, consequently I did not force her to practise and worked instead on practical challenges like intermittent times tables contests against me , and shopping trips to work out discounts, deals, change and weight differences.
3. I would not neglect the extended writing paper, as the score on this paper is doubled and will have a double the effect on the outcome compared to the verbal reasoning paper, especially as the overall pass mark does not depend on a minimum achievement on each constituent test.
All the best in September.