We had a joke: anybody who survives the "training method" is guaranteed a bright future! The important thing was to leave Zak before frustration sets in and you decide to quit chess. Valery Salov and Gata Kamsky left early and became stars in their teens...Zak religiously believed in the dogma of the classical school. In his opinion, everything young chessplayers needed to know was written in stone many years ago. - Alex Yermolinsky in The Road to Chess Improvement
Mark Taimanov said he did not think that Zak was a high-class teacher or a strong player but it was noteworthy that he did develop a lot of players with different styles and of very high class, so he must have had secret. Zak himself said he was lucky. In 1958 he was awarded the title Honored Trainer of the USSR. According to Chessmetrics when the below game was played (in which Lilienthal was absolutely destroyed by the way) Lilienthal's rating was around 2580 and in 1947 Averbach's rating was around 2470, so it's not like Zak was a non-master!
Vladimir Grigoryevich Zak (February 11, 1913 - November 25, 1994) was a Ukrainian player and one of the most famous coaches of the Soviet Union. In the 1920s the family moved to Leningrad and his named was changed from Vulf to Vladimir and he abandoned his Jewish heritage and became Russian by culture and education.
He served in the front with the Army during the Second World War and was awarded the Order of the Second-class Patriotic War, medal for service in battle and a medal for victory over Germany. After the war was over he settled in Leningrad and worked there for over 40 years as a chess coach. His best-known pupils were Boris Spassky and Viktor Korchnoi. Most of Zak's students were appreciative of his help, Yermolinsky being an exception. Zak adopted much of his teaching technique from his hero, Pyotr Romanovsky, who had made a great impression on him and with whom he had studied before World War Two.
Zak received the title of Honored Trainer of the Soviet Union in 1958. Although he himself was never able to win the title of master, his strength was the recognition of talent and its early promotion and his pupils later turned to other coaches who could develop their chess further. It should be remembered that in those days before the Elo system, you became a master in the Soviet Union only by defeating an established master in a match.
The Elo system rating distribution follows the Bell curve and because the Soviet Union had millions of players as compared to a mere handful in the US for example, they had hundreds, if not thousands of players, who by today's standards were of master strength. And, Zak did qualify to play in the semi-finals of the Soviet Championship. In 1947 he lost a match to Yuri Averbach for the master's title. In all fairness, Averbach was much more than a master, he received his GM title shortly after the match. Zak also lost a match for the title in 1948 against Viktor Vassiliev (5.5 to 7.5). Vasiliev was a strong master and analyst and an invalid due to war wounds.
Gennadi Sosonko, the Soviet-born Dutch GM, wrote that at the age of 12 he first met Zak at the Leningrad Pioneers Palace when he played Zak in s simultaneous that was designed to single out kids with potential. He remembered Zak as a stern man with Assyrian facial features (I had to Google this! - Tartajubow) and with staring unblinking dark eyes who had the habit of flexing of his jaw muscles, especially when analyzing a position.
Sosonko once asked Zak to analyze a game he (Sosonko) had won and when they arrived at the critical position and Sosonko explained that he stood worse, but his opponent was nervous and when Sosonko got into time trouble, his opponent began playing carelessly and lost. Zak got angry and called the whole affair disgraceful.
All the kids were afraid of Zak and he frequently chastised them when they wrote analysis on a sheet of paper but didn't transfer it to their notebooks in an organized fashion. Zak had a difficult personality and Sosonko believed the reason was that his life was difficult. Korchnoi, who grew up without his father who died in the war wrote that in many ways Zak replaced him and molded him as a person.
Zak was very upset when Spassky left him for Tolush; Sosonko later expressed regret that he didn't do the same thing! Still, Spassky admitted that Zak had taught him a great deal, saying he didn't think that Zak was a difficult person, but rather that he was firm in his principles.
One of Zak's questions to the youth was always who was the strongest player at the end of the 1800s. After they rattled off all the names like Steinitz and Chigorin, Zak would announce that it was James Mason and they were advised to study his games.
Eventually at the age of 73, Zak was forced to leave the Palace where he had worked for more than forty years. By that time he was also on bad terms with his colleagues, some of whom were his former pupils. In the end he suffered from senility and was moved to an old persons' home. Even then, he was interested in the latest news, looked at chess magazines and sometimes played through a game on the board.