It is imperative to integrate environmental education into school curriculum, which requires an educational change nationally. The implementation of such change can be chaotic in the beginning and thus demands highly the collaborative work of all involved actors. This study analyses how important out-of-school environmental education entities can be in helping all the main influencing factors and actors during the change s implementation. Arguments on this topic by the environmental education experts from Finland and the Netherlands are analyzed in the light of the conceptual background of both environmental education and impacting factors of an educational change. Out-of-school environmental education entities can be helpful in integrating environmental education into school subject by primarily demonstrating its need, clarity, complexity, quality and practicality; inspiring and training the teachers and principals how and what to teach, and networking with all other relevant factors such as principal, parents and local government. The co-existence of out-of-school and in-school environmental education will be strengthening each other and making environmental education more efficient.