I've been noticing a consistent pattern in scores when I go through the free practice tests; my score is always lower than I expected.

Examples:

Veritas: 630 (Q40/V38)
PR: 610 (Q39/V36)
Knewton: 640 (Q40/V39)
Kaplan: 620 (I forget my split score)

However on GMATPrep Test 1 I scored 670, and on all MGMATs I have taken so far, I score 670 on 2 and 650 on 1.

Most of my practice so far has been from the OG and to more recently, Grockit.

What do I make of the free test scores? In reading several forum posts, it seems like the scores on these introductory tests are usually lower since they expect you to get a higher percentage of questions correct. Is this the case? I'm a little demoralized (I just took PR's free test and am reeling from my 610 score) - how do I interpret these scores?

I plan on purchasing 800score's 5 tests for more practice. Is this a good idea? What's the best course of action from here? Would highly, highly appreciate any advice/tips the GMAT gurus here might have for me.

Thanks,
Kartik