امروز در مدرسه هستم و فردا به مدرسه میروم.

They’re two different verb types:

• در مدرسه هستم uses the verb بودن (هستم) to describe a state/location: I am at school.
• به مدرسه می‌روم uses the verb رفتن (می‌روم) to describe an action/movement: I go to school.

So the first clause is “being somewhere,” the second is “going somewhere.”

در means in/at and is commonly used to express location:

• در مدرسه هستم = I’m at school / in school (physically there).

You’ll also hear مدرسه‌ام or تو مدرسه‌ام in everyday speech (more colloquial), but در مدرسه هستم is clear and standard.

Because به means to and is used with movement toward a destination:

• به مدرسه می‌روم = I go to school (destination). Using در here would be incorrect because you’re not describing location; you’re describing motion.

Formally, می‌روم is present/imperfective (I go / I am going), but Persian often uses the present tense to talk about near-future plans when there’s a time word like فردا (tomorrow):

• فردا به مدرسه می‌روم = I’m going to school tomorrow.

If you want to sound more explicitly “future,” you can say:

• فردا به مدرسه خواهم رفت (more formal) = I will go to school tomorrow.

Persian often drops the subject pronoun because the verb ending shows who it is:

• هستم already means (I) am
• می‌روم already means (I) go

You can add من for emphasis or contrast:

• من امروز در مدرسه هستم و فردا به مدرسه می‌روم. = I (specifically) am at school today…

و usually means and and links two clauses:

• امروز در مدرسه هستم و فردا به مدرسه می‌روم. = Today I’m at school, and tomorrow I’m going to school.

In speech it can sound like o and sometimes functions like a softer connector (similar to and/while) depending on context, but here it’s straightforward and.

Repeating it is normal and clear. You can avoid repetition, but it changes style and sometimes clarity. Options include:

• Using a pronoun-like reference (less common for places in Persian): you’d usually just repeat.
• Restructuring: امروز در مدرسه هستم و فردا هم می‌روم. This means Today I’m at school and tomorrow I’ll go too, where می‌روم implies to school from context.

The recommended modern standard spelling is with a half-space (or hyphen in some fonts) and often with ر attached:

• می‌روم (common standard) You may also see:
• میروم (less formal / older / typing limitations)

In careful writing, می‌روم is preferred.

A common transliteration/pronunciation:

• emruz dar madrese hastam o fardâ be madrese miram

Notes:

• امروز often sounds like emruz
• فردا = fardâ
• و often sounds like o in speech

Yes. در مدرسه هستم is the normal way to say I’m at school. Saying مدرسه هستم by itself is usually incomplete/unnatural because مدرسه is a place noun and typically needs a preposition (در/تو) or another structure.

A common colloquial alternative is:

• مدرسه‌ام = literally I’m (at) school

You can swap the clauses:

• فردا به مدرسه می‌روم و امروز در مدرسه هستم. The meaning stays basically the same, but it may feel less natural because many speakers prefer chronological flow (today → tomorrow). Swapping can be used for emphasis (highlighting tomorrow first).

Persian punctuation is flexible and a comma can be added for clarity, especially in writing:

• امروز در مدرسه هستم، و فردا به مدرسه می‌روم. Many writers would even omit the comma before و, but you may see:
• امروز در مدرسه هستم و فردا به مدرسه می‌روم. (very common)

In short: punctuation is optional here; both are acceptable.

A colloquial version might be:

• امروز تو مدرسه‌ام و فردا هم می‌رم مدرسه.

Changes:

• در → تو (more conversational)
• هستم often reduces to ـم (مدرسه‌ام)
• می‌روم → می‌رم (spoken)
• هم adds too/as well, which often fits naturally in speech here