It is not only the SPCA.
Only a fraction of pounds, whether run by municipalities, the SPCA, or by private contractors have the means, the time, the resources or the know-how to test dogs under their care, to a degree of "acceptable risk", before adopting them out.

No reliable conclusions can be reached if such tests and evaluations are done:

a.
haphazardly, in a short period of time…

Even dogs, who have shown no signs of behavioral problems must be given the time, to see whether there are skeletons hidden in the closet; and to do that all dogs must be taken through a thorough evaluation. To reach a fairly accurate conclusion, the dog must be taken through numerous “real life” tests [between 50 to 100, depending on the dog and the responses] – designed for both indoor and outdoor interaction with the public and the handlers [owners] - ; over a period of no less than 5 consecutive days, lasting no more than 4 and no less than 2 hours per day; some of which must be repeated over and over until a reliable conclusion – one way or the other – is reached. A reasonable evaluation time would be between 10-15 hours per dog, over 4-5 days, at an average of 3 hours per day, testing an average of 60-70 real life issues.

b.
in an environment that is unsuitable…

such as in the back of the kennel, with the dog stuck in his cage; or exclusively on pound grounds.
All dogs must be given the opportunity to express themselves outside the pound grounds, and ideally the pound must have an area where the dog can be tested on in-house issues. Some pounds have such “real life-home” rooms where such tests can be carried out in a realistic manner.

c.
by individuals, who don’t have the experience and know-how…

The individual who will attempt such test has to have experience in these matters, preferably be a professional handler. This is not an academic task, learned in a classroom. One has to have years of experience in handling dogs, and must be very proficient in reading them as well as evaluating the results correctly.
This is not an exact science, and in fact is more of an art than science. Hence my apprehension with quickly put together rigid test methods, by desk jockeys and so-called behaviorists. These dogs must be given every chance to spill their beans, which is a very hands-on approach not preferred by most such assessors, and as such more often than not, produce inaccurate results.

One has to understand that most pounds offer Spartan facilities, operated on a shoe-string budget. Most of the individuals, who run them, cannot afford to achieve most - if any - of the above, and understandably so. The support they get – from the public, the professionals, the municipality, or their headquarters - is minimal. Their knowledge and training is generally questionable, and their motivation shaky at best. Without addressing these issues - and getting the public as well as altruistic professionals involved to a higher degree with more enthusiasm - it would be unrealistic to expect better results at both ends of the spectrum. Namely the unnecessary death of perfectly adoptable dogs, or the terrible mauling of an innocent child by one that has fallen through the cracks.