I think you need to define "effective" a bit more formally to answer this, and to state WHICH tests you're talking about.  I don't know if the two dimensions you mention are the only (or even primary) purposes of most wide-scale standard testing.

They do seem to be effective at making funding a little tiny bit more transparent, and at showing parents which school districts they should be looking for when they're choosing a city to live in.  National standardized test are somewhat effective at showing relative academic/IQ strength, to a somewhat coarse degree (very diagnostic in the middle of the range, less so in the tails).

They probably do improve education in some cases, where the teachers/curriculum would otherwise wander into unimportant topics and ineffective methods.  They almost certainly don't improve it beyond a pretty middle-of-the road level.   I think they probably help mid- and upper-level students in lower-level districts more than they help lower level students anywhere.  

For most readers of LW, if you're scoring near the top 10% of almost any standardized tests, they should mostly be ignored - the differnece betwen 90th percentile and 99th is mostly luck and approval-seeking-drive (note: this is overstated - it's also conscientiousness, IQ, and social/innate support for wanting to learn that specific material).  If you're learning out of curiosity and self-driven reasons, you're well outside the range where standardized tests can show you anything.   If you're scoring below that, then consider whether you should shift your study to include more common academic topics, or whether there are different metrics you'd prefer to measure yourself against.