The defining characteristic of a blank slater is the belief that human intelligence, personality, and physical attributes are largely trainable and conditionable. The definition of largely is of the I-know-it-when-I-see-it variety. So far as I know, there had been no formal definition of blank slater attempted by anyone who uses the term.
If you care about mine, I believe that intelligence differences in adulthood are somewhere between .6 and .8 heritable in First World countries, with the true factor most likely being toward the .8 end. See here for a short summary of the latest Minnesota Twins Studies findings.
Anyone who believes that intelligence differences are only trivially heritable, say less than .3, I would most likely consider a blank slater.
I believe that broad personality differences are about .5 heritable. Again, I would tend to classify as a blank stater anyone who believes they are significantly less than that.
I believe that there are other intellectual capacities, such as musical ability, that have a large genetic component. I know of no study that tried to measure it.
I believe that athletic abilities have a huge heritable component. Take, for example, a persons ration of fast twitch muscle fiber to slow twitch muscle fiber. That is ratio is inborn, and it has a major effect on what sports a person can be good at. I would characterize anyone who thinks a good athlete can be created by taking a random student and making him practice a lot as a blank slater, good being defined as, say, a high-school star.
I used to laugh at the people who declared that blacks average so much better in basketball than whites because blacks play so much more basketball as kids. No, white me can't jump because white men are usually born with less fast twitch fiber in their legs than people of West African descent.
Now, the average person, when asked, isn't going to be willing or able to provide his heritability estimates on demand. One can, however, recognize blank slaters by what they do. Using NCLB again as an example, one can see that the congress that passed it and the media who continue to treat NCLB's goals as reasonable are working from blank-slate assumptions.
Those who believe that different races, sexes, and ethnicities would be proportionally represented in a given job if hiring were free of discrimination are working from blank-slate premises.
Those who believe that their schools are failing black students who score about one standard deviation below white students on academic tests are working from blank slater premises.
The fact is many human differences are inborn. They are either genetic or the result of something that happened in the womb. They are intractable. Pretending it isn't so doesn't make it not so. It just gets in the way of doing things that might actually work.