El profesor es muy respetuoso con los estudiantes.

In Spanish, common nouns almost always need an article (el, la, los, las, un, una, etc.) when they refer to a specific person or thing.

• El profesor = The teacher (a specific teacher)
• Saying just Profesor es muy respetuoso… is ungrammatical in Spanish.

You can drop the article in:

• Direct address: Profesor, tengo una pregunta. – “Professor, I have a question.”
• Headlines/notes: Profesor muy respetuoso con sus estudiantes.

But in a normal full sentence describing someone, you use the article: El profesor es…

Usage varies by country, but in much of Latin America:

• Maestro / maestra

  • Often used for elementary/primary school teachers.
  • Can sound a bit more informal/affectionate in some places.

• Profesor / profesora

  • Very common for middle school, high school, and university teachers.
  • Also used more generally for instructors (sports, music, etc.).

In many contexts, especially in everyday speech, people may call nearly any teacher profe (short for profesor/a). In your sentence, El profesor sounds like a neutral, respectful way to talk about a teacher, especially beyond primary school.

Spanish uses ser for more permanent or characteristic qualities, and estar for more temporary states or conditions.

• Es muy respetuoso
  → Presenting being respectful as part of his character/personality.
  → Implies this is how he is in general.

• Está muy respetuoso
  → Would sound unusual here. In very specific contexts it might suggest a temporary or surprising level of respectfulness right now (maybe compared to usual), but this is not the normal way to describe someone’s general attitude.

So with qualities like amable, respetuoso, responsable, serio, etc., you almost always use ser:
El profesor es muy respetuoso.

• Muy = very → It modifies adjectives and adverbs.

  • muy respetuoso = very respectful

• Mucho = a lot / much / many → It modifies verbs or nouns.

  • Respeta mucho a los estudiantes. = He respects the students a lot.
  • Tiene mucho respeto por los estudiantes. = He has a lot of respect for the students.

So:

• El profesor es muy respetuoso… ✅
• El profesor es mucho respetuoso… ❌ (incorrect)

They do not mean the same thing:

• Respetuoso/a = respectful (someone who treats others with respect)

  • El profesor es muy respetuoso con los estudiantes.
    → He behaves respectfully toward the students.

• Respetable = either:

  1. Respectable (deserving respect; decent, honorable), or
  2. Quite a lot of (in quantity), in some contexts.

So:

• Un profesor respetuoso = A respectful teacher (he respects others).
• Un profesor respetable = A respectable teacher (he himself is worthy of respect).

In your sentence, we want to say he shows respect toward the students, so respetuoso is correct.

Adjectives in Spanish must agree with the gender and number of the noun they describe.

• El profesor → masculine singular
  → adjective must also be masculine singular: respetuoso.

• La profesora → feminine singular
  → La profesora es muy respetuosa con los estudiantes.

• Los profesores → masculine plural or mixed group
  → Los profesores son muy respetuosos…

• Las profesoras → feminine plural
  → Las profesoras son muy respetuosas…

Both can appear with verbs related to respect, but they are used differently.

In your sentence:

• Ser respetuoso con alguien
  
  • Focuses on the way you behave toward someone.
  • El profesor es muy respetuoso con los estudiantes.
    → His attitude and manner toward them is respectful.

With a, we typically use a different structure:

• Respetar a alguien (verb respetar
  • a)
    
    • El profesor respeta a los estudiantes.
      → He respects the students.

So:

• es respetuoso con los estudiantes ✅
• respeta a los estudiantes ✅
• es respetuoso a los estudiantes ❌ (incorrect)

You can say:

• El profesor es muy respetuoso hacia los estudiantes.

…but “con los estudiantes” is more natural and common in everyday speech.

Nuance:

• con → more neutral, standard way to express behavior toward people.
• hacia → can sound a bit more formal/written, focuses more on direction of the attitude (toward them).

For most contexts, con los estudiantes is the best choice.

Both are possible, but they say slightly different things:

• con los estudiantes

  • General: with the (group of) students (probably his students, understood from context).
  • Emphasizes students as a group more than possession.

• con sus estudiantes

  • Stresses that they are his students specifically.
  • Useful if you want to contrast with other teachers and their students.

Your original sentence does not need sus because it’s clear from context that you’re talking about the students he teaches.

Yes, there’s a nuance:

• El profesor es muy respetuoso con los estudiantes.

  • Describes his overall manner/behavior toward them.
  • Focus on his attitude/style: he speaks politely, listens, doesn’t insult, etc.

• El profesor respeta mucho a los estudiantes.

  • Focus on the fact of respecting them a lot.
  • Emphasizes degree (mucho) of respect rather than his manner.

They are close in meaning, but the first highlights how he treats them; the second highlights how much he respects them.

Yes.

• Estudiante is a common-gender noun:

  • el estudiante = male student
  • la estudiante = female student

• In the plural:

  • los estudiantes can mean:
    • all male students, or
    • a mixed group (male + female).

If you only wanted to highlight female students, some people might say las estudiantes, but los estudiantes is the usual default for mixed or unspecified groups.

Both are understood everywhere in the Spanish-speaking world:

• Estudiante(s)

  • Very common and neutral in Latin America and Spain.
  • Used for students at any level (school, university, etc.).

• Alumno(s)

  • Also widely used, especially for school-age students in many countries.
  • In some regions, it may sound a bit more traditional or institutional.

Latin American teachers and schools use both, but estudiantes is very safe, modern, and widely accepted.

Normally no. Spanish capitalizes less than English.

• Common noun (normal use):
  
  • El profesor es muy respetuoso con los estudiantes. ✅
• Even as a form of address in writing, it often stays lower-case:
  
  • Estimado profesor García:
• You only capitalize it if it’s part of a formal name of a position, course, or institution, or following specific style rules (e.g. on a plaque, official title line), but in normal text, profesor is lower-case.