Sexuality education is part of Health and Physical Education in The New Zealand Curriculum (2007) and is based on the values, principles, and concepts of the learning area. It is underpinned by the four underlying and interdependent concepts of health and physical education: hauora; a socio-ecological perspective; health promotion; and attitudes and values.
It is important to note that "Sex education" and "sexuality education" are different. The New Zealand Curriculum supports a holistic approach to sexuality education as defined by the hauora model, which includes physical, social, mental, emotional, and spiritual aspects. This is much broader than "sex education" which relates only to the physical aspects of sexual and reproductive knowledge.
Sexuality education, in particular, puberty, is a formal part of the Year 6 - 8 learning programme each year. Parents will be made aware of when this is being delivered, and may opt out of particular elements.
More detailed information around sexuality education can be found on the Ministry of Education site HERE.