The education system in Spain is well organized and consists of several stages, here is a breakdown of the age of a child in the Spanish education system:

Mandatory School Stages:

• Educación Primaria (Elementary School): This is a compulsory stage of education for children between the ages of 6 and 12. It includes elementary school, which consists of six years of education. Elementary school provides a comprehensive education covering subjects such as math, Spanish, science, history and art.
• Educación Secundaria Obligatoria (ESO) (Middle School): After completing elementary school, students move on to middle school. ESO covers 4 years of schooling and is compulsory for students between the ages of approximately 12 and 16, and is designed to further develop students' skills and prepare them for the next stage of education. It is the final stage of compulsory education in Spain. After completing it, students have the option to choose whether they want to continue their education, if so they have a choice of college or vocational school.

Optional School Stages:

• Educación Infantil (Kindergarten): Kindergarten is not mandatory, but is available for children between the ages of 3 and 6. It is an introductory stage to formal education.
• Bachillerato (High School): This is further education after completing ESO. Bachillerato lasts 2 years and is for students between the ages of about 16 and 18. It is not a compulsory stage, but it is usually required for those who wish to apply to university.
• Estudios Universitarios (University Studies): After completing Bachillerato, students can continue their education at university. Education at the university level is not mandatory and depends on the student's choice and interests.

In brief, Educación Primaria (elementary school) and Educación Secundaria Obligatoria (middle school) are compulsory for children in Spain. In contrast, kindergarten, Bachillerato and university studies are optional.

The grading scale in Spain is a range from 0 to 10, where zero is the weakest grade. To pass/fail, students must score above 5 (fractions or pluses happen). A score between 6 and 10 is considered passing, while a score between 1 and 5 is failing.

The core curriculum includes subjects such as math, Spanish, science, history, literature, foreign languages, fine arts and physical education. There are also special classes, such as religion, which are optional.

In addition to government-funded Public Education (Colegios Públicos), available to all students between the ages of 6 and 16, Spain also has a well-developed Private Education (Colegios Privados) These schools are privately funded, meaning that parents pay for their children's education. They can have different profiles, such as religious, international, or focus on special teaching methods.

Of course, there are several additional aspects to consider when describing education in Spain:

1. Registration: Before moving to Spain, it is important to register your child with the appropriate school. In some cases, it may be necessary to provide documents proving residency status.
2. Language: Spanish is the main language of instruction in most schools, so it's a good idea to familiarize your child with the basics of Spanish before starting school.
3. School Uniforms: Sometimes schools require the wearing of school uniforms, so it's a good idea to find out in advance about the requirements of the school your child will be attending.
4. Child Care: Some schools offer child care before and after school, which can be helpful for working parents.
5. School Year: The school year in Spain usually begins around September 11/15 and runs through June or July. It is divided into three semesters, with short breaks in between. This time structure allows for better planning of curricula and study and rest time for students.
6. Organization of Lessons: Unlike some education systems, Spain does not have short breaks between lessons. Instead, students have a long break of 30 minutes, usually around 12:00 p.m., which allows them to rest, eat a meal and prepare for the next class.
7. Higher Education Transition Process: Secondary school graduates must pass a matriculation exam, known as the “Selectividad,” in order to be eligible to continue their education in higher education. This exam is equivalent to a high school diploma and is a key step in the process of further education.
8. Vocational Courses: For students who prefer to get a job right after high school, there are a selection of vocational courses. These courses offer practical skills and preparation for work in a specific industry or profession.
9. University Entrance Requirements: Achieving a successful score on the matriculation exam does not guarantee automatic admission to university. Studying in Spain is competitive, and students must also take several entrance exams whose difficulty is similar to the “Selectividad” exam.
10. Study Costs: It is also worth mentioning that higher education in Spain comes with a fee. College costs vary by university and major, so students and their families need to consider these expenses when planning their education.

In summary, the education system in Spain offers a variety of options for children of different ages and educational needs. Before moving with your child, it's a good idea to gather as much information as possible about local schools and the educational options available to ensure that your child has the best possible learning and adaptation experience in the new environment.