There are two core differences between the LOMCE and the IBDP: the course structure and the type of learning encouraged.
The LOMCE will ask you to choose a study path and you will take subjects according to that path. For example, by choosing the Scientific, you will take Physics, Chemistry, and Biology instead of Geography or Philosophy. By taking the Social, you won’t be taking science courses and will instead focus on humanities. By taking the Artistic, you will do more theatre, music, and art than humanities or sciences. The LOMCE prepares you for depth of knowledge regarding an area instead of breadth of knowledge. In this aspect, it is similar to the A-Levels.
By contrast, the IBDP focuses on breadth rather than depth (although the course content is pretty detailed). In the IBDP, you will take two languages, a science class, a humanities class, a math class and a sixth class (which can be from the Arts [Group 6] or take another science or humanities course). This ensures you will build knowledge in various areas of knowledge.
LOMCE vs. IBDP
The LOMCE encourages memorization, evident in subjects like Spanish Language and Literature or History of Spain. As someone who took all four years of ESO (Obligatory Secondary Education), I found myself spewing facts off the top of my head to answer questions like “When was X written” and “Name the differences between X and Y dictatorships.” LOMCE also doesn’t encourage much essay-writing and when you are required to write one, it’s fairly short.
The IBDP, on the other hand, encourages critical thinking. You answer questions such as “How did the role of technology in WW1 impact the outcome of the war” and “How is X social group portrayed in Y book?” There’s a lot more essay-writing involved, which allows you to develop your skills as a good writer. Each IBDP subject has an Internal Assessment of about 2000 words, whereas the LOMCE has no such thing.
Both programs have similar capstone essay projects. The IBDP has the Extended Essay, a 4000-word research paper written individually, while the LOMCE has a Trabajo de Investigación, a 40-page research paper written in a group (maximum 3 people) which must be presented to a panel at the end of the second year (12th grade, or 2nd of Baccalaureate). Subject contents usually overlap, but have varying degrees of detail involved.
Both programs have their pros and cons, but I personally learned much more in the IBDP than the LOMCE. I feel that the IBDP goes the extra mile towards truly understanding what you are learning. If you prefer a more engaging, dynamic, and thorough program, take the IBDP and leave the LOMCE aside! That said, the LOMCE has its own merits and difficulties– remember, you are not less of a student if you choose LOMCE over the IBDP.