Hi
First, I've worked with more than 1800 GMAT test takers and the first thing I tell everyone of them is lose the "I'm weak in ____" mindset. Rather than painting yourself with a broad negative label, it's better to quickly get more specific about what your GAPS are with respect the quant / verbal / DI skills required to get your target score on the GMAT. That approach is more empowering and actionable -- both keys to maintaining your energy level and focus through the whole GMAT prep process.
A diagnostic session could really help to get more specific about what's keeping your math performance below where you want it. On the GMAT, gaps in Quant (also in Verbal and DI) occur at 3 levels:
1. Core skills
2. Advanced skills
3. Testing skills
One-size-fits-all programs can address the first, but the other 2 need more personalized coaching.
Whether you're deep into your prep and still struggling or just starting out, getting a "where am I right now?" assessment is key to saving prep time and maximizing your score.
Happy to discuss this further -- DM me if interested in a more specific discussion.