What is SnT condition (and why it's the best condition)

Before presenting the researchers’ findings, it can already be noted that the students’ expectations of the retained material bore no correlation to the actual results, showing that the students did not experience anything in the way of a mnemonic learning effect due to repeated practice.
The task given by the researchers (Karpicke et al) was to remember foreign language vocabulary (i.e. mashua – boat) using different methods. To properly examine specific success rates, students were divided into four groups. In the first group, students had to study and test themselves on already learned words, as well as ones they hadn’t yet memorized. This condition was referred to as ST condition (study and test). The second group didn’t study words upon initial memorization but still included those words in their practice tests, referred to as the SnT condition (exclude memorized items from study, but not from testing). This paradigm was flipped in the third group; now words committed to memory were cut from tests, however, they remained a part of study sessions (STn condition). The fourth and last group cut already learned words from practice altogether (SnTn condition).
After memorizing all word pairs, the students were excused and asked to return for a test a week later. This final test showed a clear divide between the groups: Those with the ST condition (study and test already learned items) and SnT condition (repeated testing of all items, study only not previously known items) performed strongly. Students in these groups were able to recall an average of 80% of the words provided. Compare that to the dismal outcomes of the STn condition (repeated study for all items, test only new items) and SnTn condition (cut practice for all learned items). Students in these groups were only able to recall 33% and 36% of all items, respectively.
Again, students of all groups projected a recall rate of about 50%, indicating that learners are not aware of actual impacts of different strategies.
The perhaps baffling outcome of this study is that repeated testing – and not studying – provides a great advantage in learning and especially memorizing knowledge, seeing as both groups that employed repeated testing greatly outperformed their counterparts. Between these two methods, the preferable approach is to go the route of the SnT condition (repeated testing of all items, study only the unknown ones) – simply because it significantly saves time, as the repeated studying is cut.
This discovery might seem counterintuitive, as many people, when asked, will choose repeated studying over testing. This is because testing is widely viewed merely as a neutral event, only giving insight as to what has already been memorized and what areas need further work. However, this assumption is wrong. A possible reason might be that this is what is commonly taught in schools and universities, and since predictions of success are way off regardless, students simply choose to believe this conventional wisdom.