Q: In this task, you're given passages that contain mentions of names of people, places, or things. Some of these mentions refer to the same person, place, or thing. Your job is to write questions that evaluate one's understanding of such references. Good questions are expected to link pronouns (she, her, him, his, their, etc.) or other mentions to people, places, or things to which they may refer. Do not ask questions that can be answered correctly without understanding the paragraph or having multiple answers. Avoid questions that do not link phrases referring to the same entity. For each of your questions, the answer should be one or more phrases in the paragraph, and it should be unambiguous.
Passage: Lissitzky was born on November 23, 1890 in Pochinok, a small Jewish community 50 kilometres (31 mi) southeast of Smolensk, former Russian Empire. During his childhood, he lived and studied in the city of Vitebsk, now part of Belarus, and later spent 10 years in Smolensk living with his grandparents and attending the Smolensk Grammar School, spending summer vacations in Vitebsk. Always expressing an interest and talent in drawing, he started to receive instruction at 13 from Yehuda Pen, a local Jewish artist, and by the time he was 15 was teaching students himself. In 1909, he applied to an art academy in Saint Petersburg, but was rejected. While he passed the entrance exam and was qualified, the law under the Tsarist regime only allowed a limited number of Jewish students to attend Russian schools and universities.
Like many other Jews then living in the Russian Empire, Lissitzky went to study in Germany. He left in 1909 to study architectural engineering at a Technische Hochschule in Darmstadt, Germany. During the summer of 1912, Lissitzky, in his own words, "wandered through Europe", spending time in Paris and covering 1,200 kilometres (750 mi) on foot in Italy, teaching himself about fine art and sketching architecture and landscapes that interested him. His interest in ancient Jewish culture had originated during the contacts with a Paris-based group of Russian Jews led by sculptor Ossip Zadkine, a lifetime friend of Lissitzky since early childhood, who exposed Lissitzky to conflicts between different groups within the diaspora. Also in 1912 some of his pieces were included for the first time in an exhibit by the St. Petersburg Artists Union; a notable first step. He remained in Germany until the outbreak of World War I, when he was forced to return home through Switzerland and the Balkans, along with many of his countrymen, including other expatriate artists born in the former Russian Empire, such as Wassily Kandinsky and Marc Chagall.Upon his return to Moscow, Lissitzky attended the Polytechnic Institute of Riga, which had been evacuated to Moscow because of the war, and worked for the architectural firms of Boris Velikovsky and Roman Klein.  During this work, he took an active and passionate interest in Jewish culture which, after the downfall of the openly antisemitic Tsarist regime, was experiencing a renaissance. The new Provisional Government repealed a decree that prohibited the printing of Hebrew letters and that barred Jews from citizenship. Thus Lissitzky soon devoted himself to Jewish art, exhibiting works by local Jewish artists, traveling to Mahilyow to study the traditional architecture and ornaments of old synagogues, and illustrating many Yiddish children's books. These books were Lissitzky's first major foray in book design, a field that he would greatly greatly influence over the course of his career.
A:
What was the name of the person who was teaching students by the time he was 15?