She is studying for exams that will determine which senior high school she can attend. Additional tuition at a crammer, she knows, will improve her chances of winning a place at the highest-ranked school in her district.
Millions of Japanese teenagers adopt a similar attitude. More than half the country's high-school students, aged between 13 and 18, are willing to forfeit a substantial part of their leisure time for additional schoolwork at a crammer.
A survey by the Ministry of Education in Tokyo shows that more than four million Japanese students enrolled for extra lessons at a juku in 1993. The ministry also reckons there are between 50,000 and 100,000 juku, which range from small home-based tuition services, catering for five or six students, to large multi-building organisations with tens of thousands of students.
The juku Sayaka Nakamura attends is a branch of the Tokyo-based Yoyogi Seminar. Her tuition includes classes in maths, Japanese language, social studies and the English language. She is also set regular mock tests to help her prepare for the sort of questions she will face in her senior high-school entrance exam.
Japan's largest cramming school business, the Yoyogi Seminar has 27 branches, 2,000 employees, and an annual turnover of more than Pounds 100 million.
Larger cramming schools such as the Yoyogi use computers to mark and analyse students' test scores. Sayaka's most recent report highlighed problems with Japanese grammar and recommended additional classes.
Yoyogi's "Personal Academic Search System" (PASS) also provides students with detailed information about the exams they have to sit, including such things as question preference tendencies and lowest passable marks.
Sayaka's extra lessons cost her parents about Pounds 240 a month. Her fees, plus those of her older brother, account for a major part of the Nakamuras' household expenditure. But the investment is reckoned to be a sound one. A place at a top university is the passport to a highly-paid career with one of Japan's leading companies.
The leading cramming school organisations use fax machines to send out course notes and mock exams to students unable to attend town or city-centre juku. The Yoyogi Seminar also has its own broadcasting studio for transmitting important lectures to branch schools in cities throughout Japan.
A small but growing number of juku now specialise in courses for kindergarten and elementary students. The Tokyo Gakuen juku even offers courses for two and three-year-old toddlers preparing for the entrance tests set by Japan's elite kindergarten and elementary schools.
But critics of crammers point out that not all families can afford additional tuition and several surveys show that richer children are winning an increasing proportion of the places at top universities.
Increased attendance at cramming lessons has also been linked to the deteriorating health of many young people. Studies have shown that the physical dexterity and eyesight of Japanese youngsters has declined in recent years.